[PATCH] x86: Drop KGDB support

[PATCH] x86: Drop KGDB support

[Peter Zijlstra]

KGDB does some horrible things, and with everybody having access to
virtualization these days, there is really no reason to use it over
Qemu's gdb-server.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/Kconfig                     |   2 -
 arch/x86/include/asm/kgdb.h          |  92 ----
 arch/x86/include/asm/text-patching.h |   1 -
 arch/x86/kernel/Makefile             |   1 -
 arch/x86/kernel/alternative.c        |  50 +--
 arch/x86/kernel/cpu/common.c         |  16 -
 arch/x86/kernel/early_printk.c       |   8 -
 arch/x86/kernel/kgdb.c               | 785 -----------------------------------
 arch/x86/kernel/kprobes/core.c       |  10 -
 arch/x86/kernel/kprobes/opt.c        |  11 +-
 arch/x86/kernel/traps.c              |  10 +-
 arch/x86/platform/uv/uv_nmi.c        |  76 ----
 12 files changed, 13 insertions(+), 1049 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a5e29ffd5ddc..627553e8496f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -82,7 +82,6 @@ config X86
 	select ARCH_HAS_DELAY_TIMER
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_DMA_OPS			if GART_IOMMU || XEN
-	select ARCH_HAS_EARLY_DEBUG		if KGDB
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_EXECMEM_ROX		if X86_64 && STRICT_MODULE_RWX
 	select ARCH_HAS_FAST_MULTIPLIER
@@ -198,7 +197,6 @@ config X86
 	select HAVE_ARCH_KASAN_VMALLOC		if X86_64
 	select HAVE_ARCH_KFENCE
 	select HAVE_ARCH_KMSAN			if X86_64
-	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_KSTACK_ERASE
 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
diff --git a/arch/x86/include/asm/kgdb.h b/arch/x86/include/asm/kgdb.h
deleted file mode 100644
index aacaf2502bd2..000000000000
--- a/arch/x86/include/asm/kgdb.h
+++ /dev/null
@@ -1,92 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _ASM_X86_KGDB_H
-#define _ASM_X86_KGDB_H
-
-/*
- * Copyright (C) 2001-2004 Amit S. Kale
- * Copyright (C) 2008 Wind River Systems, Inc.
- */
-
-#include <asm/ptrace.h>
-
-/*
- * BUFMAX defines the maximum number of characters in inbound/outbound
- * buffers at least NUMREGBYTES*2 are needed for register packets
- * Longer buffer is needed to list all threads
- */
-#define BUFMAX			1024
-
-/*
- *  Note that this register image is in a different order than
- *  the register image that Linux produces at interrupt time.
- *
- *  Linux's register image is defined by struct pt_regs in ptrace.h.
- *  Just why GDB uses a different order is a historical mystery.
- */
-#ifdef CONFIG_X86_32
-enum regnames {
-	GDB_AX,			/* 0 */
-	GDB_CX,			/* 1 */
-	GDB_DX,			/* 2 */
-	GDB_BX,			/* 3 */
-	GDB_SP,			/* 4 */
-	GDB_BP,			/* 5 */
-	GDB_SI,			/* 6 */
-	GDB_DI,			/* 7 */
-	GDB_PC,			/* 8 also known as eip */
-	GDB_PS,			/* 9 also known as eflags */
-	GDB_CS,			/* 10 */
-	GDB_SS,			/* 11 */
-	GDB_DS,			/* 12 */
-	GDB_ES,			/* 13 */
-	GDB_FS,			/* 14 */
-	GDB_GS,			/* 15 */
-};
-#define GDB_ORIG_AX		41
-#define DBG_MAX_REG_NUM		16
-#define NUMREGBYTES		((GDB_GS+1)*4)
-#else /* ! CONFIG_X86_32 */
-enum regnames {
-	GDB_AX,			/* 0 */
-	GDB_BX,			/* 1 */
-	GDB_CX,			/* 2 */
-	GDB_DX,			/* 3 */
-	GDB_SI,			/* 4 */
-	GDB_DI,			/* 5 */
-	GDB_BP,			/* 6 */
-	GDB_SP,			/* 7 */
-	GDB_R8,			/* 8 */
-	GDB_R9,			/* 9 */
-	GDB_R10,		/* 10 */
-	GDB_R11,		/* 11 */
-	GDB_R12,		/* 12 */
-	GDB_R13,		/* 13 */
-	GDB_R14,		/* 14 */
-	GDB_R15,		/* 15 */
-	GDB_PC,			/* 16 */
-	GDB_PS,			/* 17 */
-	GDB_CS,			/* 18 */
-	GDB_SS,			/* 19 */
-	GDB_DS,			/* 20 */
-	GDB_ES,			/* 21 */
-	GDB_FS,			/* 22 */
-	GDB_GS,			/* 23 */
-};
-#define GDB_ORIG_AX		57
-#define DBG_MAX_REG_NUM		24
-/* 17 64 bit regs and 5 32 bit regs */
-#define NUMREGBYTES		((17 * 8) + (5 * 4))
-#endif /* ! CONFIG_X86_32 */
-
-static inline void arch_kgdb_breakpoint(void)
-{
-	asm("   int $3");
-}
-#define BREAK_INSTR_SIZE	1
-#define CACHE_FLUSH_IS_SAFE	1
-#define GDB_ADJUSTS_BREAK_OFFSET
-
-extern int kgdb_ll_trap(int cmd, const char *str,
-			struct pt_regs *regs, long err, int trap, int sig);
-
-#endif /* _ASM_X86_KGDB_H */
diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index ea09381070e8..a1d284560ef8 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -33,7 +33,6 @@ extern void text_poke_apply_relocation(u8 *buf, const u8 * const instr, size_t i
  */
 extern void *text_poke(void *addr, const void *opcode, size_t len);
 extern void smp_text_poke_sync_each_cpu(void);
-extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
 extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
 #define text_poke_copy text_poke_copy
 extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 31f46fd00527..1a16af34dee3 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -128,7 +128,6 @@ obj-$(CONFIG_CRASH_DUMP)	+= crash_dump_$(BITS).o crash.o
 obj-y				+= kprobes/
 obj-$(CONFIG_MODULES)		+= module.o
 obj-$(CONFIG_X86_32)		+= doublefault_32.o
-obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_VM86)		+= vm86_32.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
 
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index efbc11f8c336..d8add52ff923 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -7,7 +7,6 @@
 #include <linux/memory.h>
 #include <linux/execmem.h>
 #include <linux/cleanup.h>
-#include <linux/kgdb.h>
 #include <linux/mmap_lock.h>
 
 #include <asm/text-patching.h>
@@ -2393,25 +2392,17 @@ static void __poke_vmalloc_pages(struct page **pages, void *addr,
 static void poke_vmalloc_pages(struct page **pages, void *addr,
 			       bool cross_page_boundary)
 {
-	if (in_dbg_master()) {
-		/*
-		 * If called from kgdb cannot sleep, but all other CPUs stopped
-		 * anyway so safe to proceed without locks
-		 */
-		__poke_vmalloc_pages(pages, addr, cross_page_boundary);
-	} else {
-		/*
-		 * execmem ROX ranges are shared between modules and can be
-		 * collapsed to huge PMD entries, and this collapse can happen
-		 * concurrently with a racing set_memory_rox().
-		 *
-		 * Prevent vmalloc_to_page() from racing by acquiring an
-		 * init_mm read lock which pairs with the init_mm write lock in
-		 * cpa_collapse_large_pages().
-		 */
-		guard(mmap_read_lock)(&init_mm);
-		__poke_vmalloc_pages(pages, addr, cross_page_boundary);
-	}
+	/*
+	 * execmem ROX ranges are shared between modules and can be
+	 * collapsed to huge PMD entries, and this collapse can happen
+	 * concurrently with a racing set_memory_rox().
+	 *
+	 * Prevent vmalloc_to_page() from racing by acquiring an
+	 * init_mm read lock which pairs with the init_mm write lock in
+	 * cpa_collapse_large_pages().
+	 */
+	guard(mmap_read_lock)(&init_mm);
+	__poke_vmalloc_pages(pages, addr, cross_page_boundary);
 }
 
 static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len)
@@ -2541,25 +2532,6 @@ void *text_poke(void *addr, const void *opcode, size_t len)
 	return __text_poke(text_poke_memcpy, addr, opcode, len);
 }
 
-/**
- * text_poke_kgdb - Update instructions on a live kernel by kgdb
- * @addr: address to modify
- * @opcode: source of the copy
- * @len: length to copy
- *
- * Only atomic text poke/set should be allowed when not doing early patching.
- * It means the size must be writable atomically and the address must be aligned
- * in a way that permits an atomic write. It also makes sure we fit on a single
- * page.
- *
- * Context: should only be used by kgdb, which ensures no other core is running,
- *	    despite the fact it does not hold the text_mutex.
- */
-void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
-{
-	return __text_poke(text_poke_memcpy, addr, opcode, len);
-}
-
 void *text_poke_copy_locked(void *addr, const void *opcode, size_t len,
 			    bool core_ok)
 {
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 9bd50c68cd7e..8a4aabcd5d60 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -18,7 +18,6 @@
 #include <linux/sched/smt.h>
 #include <linux/init.h>
 #include <linux/kprobes.h>
-#include <linux/kgdb.h>
 #include <linux/mem_encrypt.h>
 #include <linux/smp.h>
 #include <linux/cpu.h>
@@ -2340,20 +2339,6 @@ static void initialize_debug_regs(void)
 	set_debugreg(0, 0);
 }
 
-#ifdef CONFIG_KGDB
-/*
- * Restore debug regs if using kgdbwait and you have a kernel debugger
- * connection established.
- */
-static void dbg_restore_debug_regs(void)
-{
-	if (unlikely(kgdb_connected && arch_kgdb_ops.correct_hw_break))
-		arch_kgdb_ops.correct_hw_break();
-}
-#else /* ! CONFIG_KGDB */
-#define dbg_restore_debug_regs()
-#endif /* ! CONFIG_KGDB */
-
 static inline void setup_getcpu(int cpu)
 {
 	unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu));
@@ -2511,7 +2496,6 @@ void cpu_init(void)
 	load_mm_ldt(&init_mm);
 
 	initialize_debug_regs();
-	dbg_restore_debug_regs();
 
 	doublefault_init_cpu_tss();
 
diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
index cba75306e5b6..ad7534771bcf 100644
--- a/arch/x86/kernel/early_printk.c
+++ b/arch/x86/kernel/early_printk.c
@@ -46,14 +46,6 @@ static void early_vga_write(struct console *con, const char *str, unsigned n)
 				writew(0x720, VGABASE + 2*(max_xpos*j + i));
 			current_ypos = max_ypos-1;
 		}
-#ifdef CONFIG_KGDB_KDB
-		if (c == '\b') {
-			if (current_xpos > 0)
-				current_xpos--;
-		} else if (c == '\r') {
-			current_xpos = 0;
-		} else
-#endif
 		if (c == '\n') {
 			current_xpos = 0;
 			current_ypos++;
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
deleted file mode 100644
index 96af1242454e..000000000000
--- a/arch/x86/kernel/kgdb.c
+++ /dev/null
@@ -1,785 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- */
-
-/*
- * Copyright (C) 2004 Amit S. Kale <amitkale@linsyssoft.com>
- * Copyright (C) 2000-2001 VERITAS Software Corporation.
- * Copyright (C) 2002 Andi Kleen, SuSE Labs
- * Copyright (C) 2004 LinSysSoft Technologies Pvt. Ltd.
- * Copyright (C) 2007 MontaVista Software, Inc.
- * Copyright (C) 2007-2008 Jason Wessel, Wind River Systems, Inc.
- */
-/****************************************************************************
- *  Contributor:     Lake Stevens Instrument Division$
- *  Written by:      Glenn Engel $
- *  Updated by:	     Amit Kale<akale@veritas.com>
- *  Updated by:	     Tom Rini <trini@kernel.crashing.org>
- *  Updated by:	     Jason Wessel <jason.wessel@windriver.com>
- *  Modified for 386 by Jim Kingdon, Cygnus Support.
- *  Original kgdb, compatibility with 2.1.xx kernel by
- *  David Grothe <dave@gcom.com>
- *  Integrated into 2.2.5 kernel by Tigran Aivazian <tigran@sco.com>
- *  X86_64 changes from Andi Kleen's patch merged by Jim Houston
- */
-#include <linux/spinlock.h>
-#include <linux/kdebug.h>
-#include <linux/string.h>
-#include <linux/kernel.h>
-#include <linux/ptrace.h>
-#include <linux/sched.h>
-#include <linux/delay.h>
-#include <linux/kgdb.h>
-#include <linux/smp.h>
-#include <linux/nmi.h>
-#include <linux/hw_breakpoint.h>
-#include <linux/uaccess.h>
-#include <linux/memory.h>
-
-#include <asm/text-patching.h>
-#include <asm/debugreg.h>
-#include <asm/apicdef.h>
-#include <asm/apic.h>
-#include <asm/nmi.h>
-#include <asm/switch_to.h>
-
-struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
-{
-#ifdef CONFIG_X86_32
-	{ "ax", 4, offsetof(struct pt_regs, ax) },
-	{ "cx", 4, offsetof(struct pt_regs, cx) },
-	{ "dx", 4, offsetof(struct pt_regs, dx) },
-	{ "bx", 4, offsetof(struct pt_regs, bx) },
-	{ "sp", 4, offsetof(struct pt_regs, sp) },
-	{ "bp", 4, offsetof(struct pt_regs, bp) },
-	{ "si", 4, offsetof(struct pt_regs, si) },
-	{ "di", 4, offsetof(struct pt_regs, di) },
-	{ "ip", 4, offsetof(struct pt_regs, ip) },
-	{ "flags", 4, offsetof(struct pt_regs, flags) },
-	{ "cs", 4, offsetof(struct pt_regs, cs) },
-	{ "ss", 4, offsetof(struct pt_regs, ss) },
-	{ "ds", 4, offsetof(struct pt_regs, ds) },
-	{ "es", 4, offsetof(struct pt_regs, es) },
-#else
-	{ "ax", 8, offsetof(struct pt_regs, ax) },
-	{ "bx", 8, offsetof(struct pt_regs, bx) },
-	{ "cx", 8, offsetof(struct pt_regs, cx) },
-	{ "dx", 8, offsetof(struct pt_regs, dx) },
-	{ "si", 8, offsetof(struct pt_regs, si) },
-	{ "di", 8, offsetof(struct pt_regs, di) },
-	{ "bp", 8, offsetof(struct pt_regs, bp) },
-	{ "sp", 8, offsetof(struct pt_regs, sp) },
-	{ "r8", 8, offsetof(struct pt_regs, r8) },
-	{ "r9", 8, offsetof(struct pt_regs, r9) },
-	{ "r10", 8, offsetof(struct pt_regs, r10) },
-	{ "r11", 8, offsetof(struct pt_regs, r11) },
-	{ "r12", 8, offsetof(struct pt_regs, r12) },
-	{ "r13", 8, offsetof(struct pt_regs, r13) },
-	{ "r14", 8, offsetof(struct pt_regs, r14) },
-	{ "r15", 8, offsetof(struct pt_regs, r15) },
-	{ "ip", 8, offsetof(struct pt_regs, ip) },
-	{ "flags", 4, offsetof(struct pt_regs, flags) },
-	{ "cs", 4, offsetof(struct pt_regs, cs) },
-	{ "ss", 4, offsetof(struct pt_regs, ss) },
-	{ "ds", 4, -1 },
-	{ "es", 4, -1 },
-#endif
-	{ "fs", 4, -1 },
-	{ "gs", 4, -1 },
-};
-
-int dbg_set_reg(int regno, void *mem, struct pt_regs *regs)
-{
-	if (
-#ifdef CONFIG_X86_32
-	    regno == GDB_SS || regno == GDB_FS || regno == GDB_GS ||
-#endif
-	    regno == GDB_SP || regno == GDB_ORIG_AX)
-		return 0;
-
-	if (dbg_reg_def[regno].offset != -1)
-		memcpy((void *)regs + dbg_reg_def[regno].offset, mem,
-		       dbg_reg_def[regno].size);
-	return 0;
-}
-
-char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs)
-{
-	if (regno == GDB_ORIG_AX) {
-		memcpy(mem, &regs->orig_ax, sizeof(regs->orig_ax));
-		return "orig_ax";
-	}
-	if (regno >= DBG_MAX_REG_NUM || regno < 0)
-		return NULL;
-
-	if (dbg_reg_def[regno].offset != -1)
-		memcpy(mem, (void *)regs + dbg_reg_def[regno].offset,
-		       dbg_reg_def[regno].size);
-
-#ifdef CONFIG_X86_32
-	switch (regno) {
-	case GDB_GS:
-	case GDB_FS:
-		*(unsigned long *)mem = 0xFFFF;
-		break;
-	}
-#endif
-	return dbg_reg_def[regno].name;
-}
-
-/**
- *	sleeping_thread_to_gdb_regs - Convert ptrace regs to GDB regs
- *	@gdb_regs: A pointer to hold the registers in the order GDB wants.
- *	@p: The &struct task_struct of the desired process.
- *
- *	Convert the register values of the sleeping process in @p to
- *	the format that GDB expects.
- *	This function is called when kgdb does not have access to the
- *	&struct pt_regs and therefore it should fill the gdb registers
- *	@gdb_regs with what has	been saved in &struct thread_struct
- *	thread field during switch_to.
- */
-void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
-{
-#ifndef CONFIG_X86_32
-	u32 *gdb_regs32 = (u32 *)gdb_regs;
-#endif
-	gdb_regs[GDB_AX]	= 0;
-	gdb_regs[GDB_BX]	= 0;
-	gdb_regs[GDB_CX]	= 0;
-	gdb_regs[GDB_DX]	= 0;
-	gdb_regs[GDB_SI]	= 0;
-	gdb_regs[GDB_DI]	= 0;
-	gdb_regs[GDB_BP]	= ((struct inactive_task_frame *)p->thread.sp)->bp;
-#ifdef CONFIG_X86_32
-	gdb_regs[GDB_DS]	= __KERNEL_DS;
-	gdb_regs[GDB_ES]	= __KERNEL_DS;
-	gdb_regs[GDB_PS]	= 0;
-	gdb_regs[GDB_CS]	= __KERNEL_CS;
-	gdb_regs[GDB_SS]	= __KERNEL_DS;
-	gdb_regs[GDB_FS]	= 0xFFFF;
-	gdb_regs[GDB_GS]	= 0xFFFF;
-#else
-	gdb_regs32[GDB_PS]	= 0;
-	gdb_regs32[GDB_CS]	= __KERNEL_CS;
-	gdb_regs32[GDB_SS]	= __KERNEL_DS;
-	gdb_regs[GDB_R8]	= 0;
-	gdb_regs[GDB_R9]	= 0;
-	gdb_regs[GDB_R10]	= 0;
-	gdb_regs[GDB_R11]	= 0;
-	gdb_regs[GDB_R12]	= 0;
-	gdb_regs[GDB_R13]	= 0;
-	gdb_regs[GDB_R14]	= 0;
-	gdb_regs[GDB_R15]	= 0;
-#endif
-	gdb_regs[GDB_PC]	= 0;
-	gdb_regs[GDB_SP]	= p->thread.sp;
-}
-
-static struct hw_breakpoint {
-	unsigned		enabled;
-	unsigned long		addr;
-	int			len;
-	int			type;
-	struct perf_event	* __percpu *pev;
-} breakinfo[HBP_NUM];
-
-static unsigned long early_dr7;
-
-static void kgdb_correct_hw_break(void)
-{
-	int breakno;
-
-	for (breakno = 0; breakno < HBP_NUM; breakno++) {
-		struct perf_event *bp;
-		struct arch_hw_breakpoint *info;
-		int val;
-		int cpu = raw_smp_processor_id();
-		if (!breakinfo[breakno].enabled)
-			continue;
-		if (dbg_is_early) {
-			set_debugreg(breakinfo[breakno].addr, breakno);
-			early_dr7 |= encode_dr7(breakno,
-						breakinfo[breakno].len,
-						breakinfo[breakno].type);
-			set_debugreg(early_dr7, 7);
-			continue;
-		}
-		bp = *per_cpu_ptr(breakinfo[breakno].pev, cpu);
-		info = counter_arch_bp(bp);
-		if (bp->attr.disabled != 1)
-			continue;
-		bp->attr.bp_addr = breakinfo[breakno].addr;
-		bp->attr.bp_len = breakinfo[breakno].len;
-		bp->attr.bp_type = breakinfo[breakno].type;
-		info->address = breakinfo[breakno].addr;
-		info->len = breakinfo[breakno].len;
-		info->type = breakinfo[breakno].type;
-		val = arch_install_hw_breakpoint(bp);
-		if (!val)
-			bp->attr.disabled = 0;
-	}
-	if (!dbg_is_early)
-		hw_breakpoint_restore();
-}
-
-static int hw_break_reserve_slot(int breakno)
-{
-	int cpu;
-	int cnt = 0;
-	struct perf_event **pevent;
-
-	if (dbg_is_early)
-		return 0;
-
-	for_each_online_cpu(cpu) {
-		cnt++;
-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
-		if (dbg_reserve_bp_slot(*pevent))
-			goto fail;
-	}
-
-	return 0;
-
-fail:
-	for_each_online_cpu(cpu) {
-		cnt--;
-		if (!cnt)
-			break;
-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
-		dbg_release_bp_slot(*pevent);
-	}
-	return -1;
-}
-
-static int hw_break_release_slot(int breakno)
-{
-	struct perf_event **pevent;
-	int cpu;
-
-	if (dbg_is_early)
-		return 0;
-
-	for_each_online_cpu(cpu) {
-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
-		if (dbg_release_bp_slot(*pevent))
-			/*
-			 * The debugger is responsible for handing the retry on
-			 * remove failure.
-			 */
-			return -1;
-	}
-	return 0;
-}
-
-static int
-kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
-{
-	int i;
-
-	for (i = 0; i < HBP_NUM; i++)
-		if (breakinfo[i].addr == addr && breakinfo[i].enabled)
-			break;
-	if (i == HBP_NUM)
-		return -1;
-
-	if (hw_break_release_slot(i)) {
-		printk(KERN_ERR "Cannot remove hw breakpoint at %lx\n", addr);
-		return -1;
-	}
-	breakinfo[i].enabled = 0;
-
-	return 0;
-}
-
-static void kgdb_remove_all_hw_break(void)
-{
-	int i;
-	int cpu = raw_smp_processor_id();
-	struct perf_event *bp;
-
-	for (i = 0; i < HBP_NUM; i++) {
-		if (!breakinfo[i].enabled)
-			continue;
-		bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
-		if (!bp->attr.disabled) {
-			arch_uninstall_hw_breakpoint(bp);
-			bp->attr.disabled = 1;
-			continue;
-		}
-		if (dbg_is_early)
-			early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
-						 breakinfo[i].type);
-		else if (hw_break_release_slot(i))
-			printk(KERN_ERR "KGDB: hw bpt remove failed %lx\n",
-			       breakinfo[i].addr);
-		breakinfo[i].enabled = 0;
-	}
-}
-
-static int
-kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
-{
-	int i;
-
-	for (i = 0; i < HBP_NUM; i++)
-		if (!breakinfo[i].enabled)
-			break;
-	if (i == HBP_NUM)
-		return -1;
-
-	switch (bptype) {
-	case BP_HARDWARE_BREAKPOINT:
-		len = 1;
-		breakinfo[i].type = X86_BREAKPOINT_EXECUTE;
-		break;
-	case BP_WRITE_WATCHPOINT:
-		breakinfo[i].type = X86_BREAKPOINT_WRITE;
-		break;
-	case BP_ACCESS_WATCHPOINT:
-		breakinfo[i].type = X86_BREAKPOINT_RW;
-		break;
-	default:
-		return -1;
-	}
-	switch (len) {
-	case 1:
-		breakinfo[i].len = X86_BREAKPOINT_LEN_1;
-		break;
-	case 2:
-		breakinfo[i].len = X86_BREAKPOINT_LEN_2;
-		break;
-	case 4:
-		breakinfo[i].len = X86_BREAKPOINT_LEN_4;
-		break;
-#ifdef CONFIG_X86_64
-	case 8:
-		breakinfo[i].len = X86_BREAKPOINT_LEN_8;
-		break;
-#endif
-	default:
-		return -1;
-	}
-	breakinfo[i].addr = addr;
-	if (hw_break_reserve_slot(i)) {
-		breakinfo[i].addr = 0;
-		return -1;
-	}
-	breakinfo[i].enabled = 1;
-
-	return 0;
-}
-
-/**
- *	kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
- *	@regs: Current &struct pt_regs.
- *
- *	This function will be called if the particular architecture must
- *	disable hardware debugging while it is processing gdb packets or
- *	handling exception.
- */
-static void kgdb_disable_hw_debug(struct pt_regs *regs)
-{
-	int i;
-	int cpu = raw_smp_processor_id();
-	struct perf_event *bp;
-
-	/* Disable hardware debugging while we are in kgdb: */
-	set_debugreg(DR7_FIXED_1, 7);
-	for (i = 0; i < HBP_NUM; i++) {
-		if (!breakinfo[i].enabled)
-			continue;
-		if (dbg_is_early) {
-			early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
-						 breakinfo[i].type);
-			continue;
-		}
-		bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
-		if (bp->attr.disabled == 1)
-			continue;
-		arch_uninstall_hw_breakpoint(bp);
-		bp->attr.disabled = 1;
-	}
-}
-
-#ifdef CONFIG_SMP
-/**
- *	kgdb_roundup_cpus - Get other CPUs into a holding pattern
- *
- *	On SMP systems, we need to get the attention of the other CPUs
- *	and get them into a known state.  This should do what is needed
- *	to get the other CPUs to call kgdb_handle_exception().  Note that
- *	on some arches, the NMI approach is not used for rounding up all
- *	the CPUs.  For example, in case of MIPS, smp_call_function() is
- *	used to roundup CPUs.
- *
- *	On non-SMP systems, this is not called.
- */
-void kgdb_roundup_cpus(void)
-{
-	apic_send_IPI_allbutself(NMI_VECTOR);
-}
-#endif
-
-/**
- *	kgdb_arch_handle_exception - Handle architecture specific GDB packets.
- *	@e_vector: The error vector of the exception that happened.
- *	@signo: The signal number of the exception that happened.
- *	@err_code: The error code of the exception that happened.
- *	@remcomInBuffer: The buffer of the packet we have read.
- *	@remcomOutBuffer: The buffer of %BUFMAX bytes to write a packet into.
- *	@linux_regs: The &struct pt_regs of the current process.
- *
- *	This function MUST handle the 'c' and 's' command packets,
- *	as well packets to set / remove a hardware breakpoint, if used.
- *	If there are additional packets which the hardware needs to handle,
- *	they are handled here.  The code should return -1 if it wants to
- *	process more packets, and a %0 or %1 if it wants to exit from the
- *	kgdb callback.
- */
-int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
-			       char *remcomInBuffer, char *remcomOutBuffer,
-			       struct pt_regs *linux_regs)
-{
-	unsigned long addr;
-	char *ptr;
-
-	switch (remcomInBuffer[0]) {
-	case 'c':
-	case 's':
-		/* try to read optional parameter, pc unchanged if no parm */
-		ptr = &remcomInBuffer[1];
-		if (kgdb_hex2long(&ptr, &addr))
-			linux_regs->ip = addr;
-		fallthrough;
-	case 'D':
-	case 'k':
-		/* clear the trace bit */
-		linux_regs->flags &= ~X86_EFLAGS_TF;
-		atomic_set(&kgdb_cpu_doing_single_step, -1);
-
-		/* set the trace bit if we're stepping */
-		if (remcomInBuffer[0] == 's') {
-			linux_regs->flags |= X86_EFLAGS_TF;
-			atomic_set(&kgdb_cpu_doing_single_step,
-				   raw_smp_processor_id());
-		}
-
-		return 0;
-	}
-
-	/* this means that we do not want to exit from the handler: */
-	return -1;
-}
-
-static inline int
-single_step_cont(struct pt_regs *regs, struct die_args *args)
-{
-	/*
-	 * Single step exception from kernel space to user space so
-	 * eat the exception and continue the process:
-	 */
-	printk(KERN_ERR "KGDB: trap/step from kernel to user space, "
-			"resuming...\n");
-	kgdb_arch_handle_exception(args->trapnr, args->signr,
-				   args->err, "c", "", regs);
-	/*
-	 * Reset the BS bit in dr6 (pointed by args->err) to
-	 * denote completion of processing
-	 */
-	(*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
-
-	return NOTIFY_STOP;
-}
-
-static DECLARE_BITMAP(was_in_debug_nmi, NR_CPUS);
-
-static int kgdb_nmi_handler(unsigned int cmd, struct pt_regs *regs)
-{
-	int cpu;
-
-	switch (cmd) {
-	case NMI_LOCAL:
-		if (atomic_read(&kgdb_active) != -1) {
-			/* KGDB CPU roundup */
-			cpu = raw_smp_processor_id();
-			kgdb_nmicallback(cpu, regs);
-			set_bit(cpu, was_in_debug_nmi);
-			touch_nmi_watchdog();
-
-			return NMI_HANDLED;
-		}
-		break;
-
-	case NMI_UNKNOWN:
-		cpu = raw_smp_processor_id();
-
-		if (__test_and_clear_bit(cpu, was_in_debug_nmi))
-			return NMI_HANDLED;
-
-		break;
-	default:
-		/* do nothing */
-		break;
-	}
-	return NMI_DONE;
-}
-
-static int __kgdb_notify(struct die_args *args, unsigned long cmd)
-{
-	struct pt_regs *regs = args->regs;
-
-	switch (cmd) {
-	case DIE_DEBUG:
-		if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
-			if (user_mode(regs))
-				return single_step_cont(regs, args);
-			break;
-		} else if (test_thread_flag(TIF_SINGLESTEP))
-			/* This means a user thread is single stepping
-			 * a system call which should be ignored
-			 */
-			return NOTIFY_DONE;
-		fallthrough;
-	default:
-		if (user_mode(regs))
-			return NOTIFY_DONE;
-	}
-
-	if (kgdb_handle_exception(args->trapnr, args->signr, cmd, regs))
-		return NOTIFY_DONE;
-
-	/* Must touch watchdog before return to normal operation */
-	touch_nmi_watchdog();
-	return NOTIFY_STOP;
-}
-
-int kgdb_ll_trap(int cmd, const char *str,
-		 struct pt_regs *regs, long err, int trap, int sig)
-{
-	struct die_args args = {
-		.regs	= regs,
-		.str	= str,
-		.err	= err,
-		.trapnr	= trap,
-		.signr	= sig,
-
-	};
-
-	if (!kgdb_io_module_registered)
-		return NOTIFY_DONE;
-
-	return __kgdb_notify(&args, cmd);
-}
-
-static int
-kgdb_notify(struct notifier_block *self, unsigned long cmd, void *ptr)
-{
-	unsigned long flags;
-	int ret;
-
-	local_irq_save(flags);
-	ret = __kgdb_notify(ptr, cmd);
-	local_irq_restore(flags);
-
-	return ret;
-}
-
-static struct notifier_block kgdb_notifier = {
-	.notifier_call	= kgdb_notify,
-};
-
-/**
- *	kgdb_arch_init - Perform any architecture specific initialization.
- *
- *	This function will handle the initialization of any architecture
- *	specific callbacks.
- */
-int kgdb_arch_init(void)
-{
-	int retval;
-
-	retval = register_die_notifier(&kgdb_notifier);
-	if (retval)
-		goto out;
-
-	retval = register_nmi_handler(NMI_LOCAL, kgdb_nmi_handler,
-					0, "kgdb");
-	if (retval)
-		goto out1;
-
-	retval = register_nmi_handler(NMI_UNKNOWN, kgdb_nmi_handler,
-					0, "kgdb");
-
-	if (retval)
-		goto out2;
-
-	return retval;
-
-out2:
-	unregister_nmi_handler(NMI_LOCAL, "kgdb");
-out1:
-	unregister_die_notifier(&kgdb_notifier);
-out:
-	return retval;
-}
-
-static void kgdb_hw_overflow_handler(struct perf_event *event,
-		struct perf_sample_data *data, struct pt_regs *regs)
-{
-	struct task_struct *tsk = current;
-	int i;
-
-	for (i = 0; i < 4; i++) {
-		if (breakinfo[i].enabled)
-			tsk->thread.virtual_dr6 |= (DR_TRAP0 << i);
-	}
-}
-
-void kgdb_arch_late(void)
-{
-	int i, cpu;
-	struct perf_event_attr attr;
-	struct perf_event **pevent;
-
-	/*
-	 * Pre-allocate the hw breakpoint instructions in the non-atomic
-	 * portion of kgdb because this operation requires mutexs to
-	 * complete.
-	 */
-	hw_breakpoint_init(&attr);
-	attr.bp_addr = (unsigned long)kgdb_arch_init;
-	attr.bp_len = HW_BREAKPOINT_LEN_1;
-	attr.bp_type = HW_BREAKPOINT_W;
-	attr.disabled = 1;
-	for (i = 0; i < HBP_NUM; i++) {
-		if (breakinfo[i].pev)
-			continue;
-		breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL, NULL);
-		if (IS_ERR_PCPU(breakinfo[i].pev)) {
-			printk(KERN_ERR "kgdb: Could not allocate hw"
-			       "breakpoints\nDisabling the kernel debugger\n");
-			breakinfo[i].pev = NULL;
-			kgdb_arch_exit();
-			return;
-		}
-		for_each_online_cpu(cpu) {
-			pevent = per_cpu_ptr(breakinfo[i].pev, cpu);
-			pevent[0]->hw.sample_period = 1;
-			pevent[0]->overflow_handler = kgdb_hw_overflow_handler;
-			if (pevent[0]->destroy != NULL) {
-				pevent[0]->destroy = NULL;
-				release_bp_slot(*pevent);
-			}
-		}
-	}
-}
-
-/**
- *	kgdb_arch_exit - Perform any architecture specific uninitalization.
- *
- *	This function will handle the uninitalization of any architecture
- *	specific callbacks, for dynamic registration and unregistration.
- */
-void kgdb_arch_exit(void)
-{
-	int i;
-	for (i = 0; i < 4; i++) {
-		if (breakinfo[i].pev) {
-			unregister_wide_hw_breakpoint(breakinfo[i].pev);
-			breakinfo[i].pev = NULL;
-		}
-	}
-	unregister_nmi_handler(NMI_UNKNOWN, "kgdb");
-	unregister_nmi_handler(NMI_LOCAL, "kgdb");
-	unregister_die_notifier(&kgdb_notifier);
-}
-
-/**
- *	kgdb_skipexception - Bail out of KGDB when we've been triggered.
- *	@exception: Exception vector number
- *	@regs: Current &struct pt_regs.
- *
- *	On some architectures we need to skip a breakpoint exception when
- *	it occurs after a breakpoint has been removed.
- *
- * Skip an int3 exception when it occurs after a breakpoint has been
- * removed. Backtrack eip by 1 since the int3 would have caused it to
- * increment by 1.
- */
-int kgdb_skipexception(int exception, struct pt_regs *regs)
-{
-	if (exception == 3 && kgdb_isremovedbreak(regs->ip - 1)) {
-		regs->ip -= 1;
-		return 1;
-	}
-	return 0;
-}
-
-unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs)
-{
-	if (exception == 3)
-		return instruction_pointer(regs) - 1;
-	return instruction_pointer(regs);
-}
-
-void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
-{
-	regs->ip = ip;
-}
-
-int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
-{
-	int err;
-
-	bpt->type = BP_BREAKPOINT;
-	err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
-				BREAK_INSTR_SIZE);
-	if (err)
-		return err;
-	err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
-				 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
-	if (!err)
-		return err;
-	/*
-	 * It is safe to call text_poke_kgdb() because normal kernel execution
-	 * is stopped on all cores, so long as the text_mutex is not locked.
-	 */
-	if (mutex_is_locked(&text_mutex))
-		return -EBUSY;
-	text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
-		       BREAK_INSTR_SIZE);
-	bpt->type = BP_POKE_BREAKPOINT;
-
-	return 0;
-}
-
-int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
-{
-	if (bpt->type != BP_POKE_BREAKPOINT)
-		goto knl_write;
-	/*
-	 * It is safe to call text_poke_kgdb() because normal kernel execution
-	 * is stopped on all cores, so long as the text_mutex is not locked.
-	 */
-	if (mutex_is_locked(&text_mutex))
-		goto knl_write;
-	text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
-		       BREAK_INSTR_SIZE);
-	return 0;
-
-knl_write:
-	return copy_to_kernel_nofault((char *)bpt->bpt_addr,
-				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
-}
-
-const struct kgdb_arch arch_kgdb_ops = {
-	/* Breakpoint instruction: */
-	.gdb_bpt_instr		= { 0xcc },
-	.flags			= KGDB_HW_BREAKPOINT,
-	.set_hw_breakpoint	= kgdb_set_hw_break,
-	.remove_hw_breakpoint	= kgdb_remove_hw_break,
-	.disable_hw_break	= kgdb_disable_hw_debug,
-	.remove_all_hw_break	= kgdb_remove_all_hw_break,
-	.correct_hw_break	= kgdb_correct_hw_break,
-};
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 133ff20caccd..65707e4cffae 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -37,7 +37,6 @@
 #include <linux/extable.h>
 #include <linux/kdebug.h>
 #include <linux/kallsyms.h>
-#include <linux/kgdb.h>
 #include <linux/ftrace.h>
 #include <linux/kasan.h>
 #include <linux/objtool.h>
@@ -311,15 +310,6 @@ static bool can_probe(unsigned long paddr)
 		if (insn_decode_kernel(&insn, (void *)__addr) < 0)
 			return false;
 
-#ifdef CONFIG_KGDB
-		/*
-		 * If there is a dynamically installed kgdb sw breakpoint,
-		 * this function should not be probed.
-		 */
-		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
-		    kgdb_has_hit_break(addr))
-			return false;
-#endif
 		addr += insn.length;
 	}
 
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 3f8fea52619f..821a416faf67 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -15,7 +15,6 @@
 #include <linux/extable.h>
 #include <linux/kdebug.h>
 #include <linux/kallsyms.h>
-#include <linux/kgdb.h>
 #include <linux/ftrace.h>
 #include <linux/objtool.h>
 #include <linux/pgtable.h>
@@ -297,15 +296,7 @@ static int can_optimize(unsigned long paddr)
 		ret = insn_decode_kernel(&insn, (void *)recovered_insn);
 		if (ret < 0)
 			return 0;
-#ifdef CONFIG_KGDB
-		/*
-		 * If there is a dynamically installed kgdb sw breakpoint,
-		 * this function should not be probed.
-		 */
-		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
-		    kgdb_has_hit_break(addr))
-			return 0;
-#endif
+
 		/* Recover address */
 		insn.kaddr = (void *)addr;
 		insn.next_byte = (void *)(addr + insn.length);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 30aa8369957e..20a1fa62d5b2 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -20,7 +20,6 @@
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
 #include <linux/kdebug.h>
-#include <linux/kgdb.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/ptrace.h>
@@ -975,12 +974,6 @@ static bool do_int3(struct pt_regs *regs)
 {
 	int res;
 
-#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
-	if (kgdb_ll_trap(DIE_INT3, "int3", regs, 0, X86_TRAP_BP,
-			 SIGTRAP) == NOTIFY_STOP)
-		return true;
-#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
-
 #ifdef CONFIG_KPROBES
 	if (kprobe_int3_handler(regs))
 		return true;
@@ -1205,7 +1198,7 @@ static bool notify_debug(struct pt_regs *regs, unsigned long *dr6)
 	 * consumed - hw_breakpoint_handler(), single_stop_cont().
 	 *
 	 * Notifiers will set bits in @virtual_dr6 to indicate the desire
-	 * for signals - ptrace_triggered(), kgdb_hw_overflow_handler().
+	 * for signals - ptrace_triggered().
 	 */
 	if (notify_die(DIE_DEBUG, "debug", regs, (long)dr6, 0, SIGTRAP) == NOTIFY_STOP)
 		return true;
@@ -1276,7 +1269,6 @@ static noinstr void exc_debug_kernel(struct pt_regs *regs, unsigned long dr6)
 	 * The kernel doesn't use TF single-step outside of:
 	 *
 	 *  - Kprobes, consumed through kprobe_debug_handler()
-	 *  - KGDB, consumed through notify_debug()
 	 *
 	 * So if we get here with DR_STEP set, something is wonky.
 	 *
diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c
index 565ab43fa6b4..7d8a16945900 100644
--- a/arch/x86/platform/uv/uv_nmi.c
+++ b/arch/x86/platform/uv/uv_nmi.c
@@ -9,9 +9,7 @@
 
 #include <linux/cpu.h>
 #include <linux/delay.h>
-#include <linux/kdb.h>
 #include <linux/kexec.h>
-#include <linux/kgdb.h>
 #include <linux/moduleparam.h>
 #include <linux/nmi.h>
 #include <linux/sched.h>
@@ -184,8 +182,6 @@ enum action_t {
 	nmi_act_kdump,
 	nmi_act_dump,
 	nmi_act_ips,
-	nmi_act_kdb,
-	nmi_act_kgdb,
 	nmi_act_health,
 	nmi_act_max
 };
@@ -194,8 +190,6 @@ static const char * const actions[nmi_act_max] = {
 	[nmi_act_kdump] = "kdump",
 	[nmi_act_dump] = "dump",
 	[nmi_act_ips] = "ips",
-	[nmi_act_kdb] = "kdb",
-	[nmi_act_kgdb] = "kgdb",
 	[nmi_act_health] = "health",
 };
 
@@ -203,8 +197,6 @@ static const char * const actions_desc[nmi_act_max] = {
 	[nmi_act_kdump] = "do kernel crash dump",
 	[nmi_act_dump] = "dump process stack for each cpu",
 	[nmi_act_ips] = "dump Inst Ptr info for each cpu",
-	[nmi_act_kdb] = "enter KDB (needs kgdboc= assignment)",
-	[nmi_act_kgdb] = "enter KGDB (needs gdb target remote)",
 	[nmi_act_health] = "check if CPUs respond to NMI",
 };
 
@@ -868,70 +860,6 @@ static void uv_nmi_kdump(int cpu, int main, struct pt_regs *regs)
 	}
 }
 
-#ifdef CONFIG_KGDB
-#ifdef CONFIG_KGDB_KDB
-static inline int uv_nmi_kdb_reason(void)
-{
-	return KDB_REASON_SYSTEM_NMI;
-}
-#else /* !CONFIG_KGDB_KDB */
-static inline int uv_nmi_kdb_reason(void)
-{
-	/* Ensure user is expecting to attach gdb remote */
-	if (uv_nmi_action == nmi_act_kgdb)
-		return 0;
-
-	pr_err("UV: NMI error: KDB is not enabled in this kernel\n");
-	return -1;
-}
-#endif /* CONFIG_KGDB_KDB */
-
-/*
- * Call KGDB/KDB from NMI handler
- *
- * Note that if both KGDB and KDB are configured, then the action of 'kgdb' or
- * 'kdb' has no affect on which is used.  See the KGDB documentation for further
- * information.
- */
-static void uv_call_kgdb_kdb(int cpu, struct pt_regs *regs, int master)
-{
-	if (master) {
-		int reason = uv_nmi_kdb_reason();
-		int ret;
-
-		if (reason < 0)
-			return;
-
-		/* Call KGDB NMI handler as MASTER */
-		ret = kgdb_nmicallin(cpu, X86_TRAP_NMI, regs, reason,
-				&uv_nmi_slave_continue);
-		if (ret) {
-			pr_alert("KGDB returned error, is kgdboc set?\n");
-			atomic_set(&uv_nmi_slave_continue, SLAVE_EXIT);
-		}
-	} else {
-		/* Wait for KGDB signal that it's ready for slaves to enter */
-		int sig;
-
-		do {
-			cpu_relax();
-			sig = atomic_read(&uv_nmi_slave_continue);
-		} while (!sig);
-
-		/* Call KGDB as slave */
-		if (sig == SLAVE_CONTINUE)
-			kgdb_nmicallback(cpu, regs);
-	}
-	uv_nmi_sync_exit(master);
-}
-
-#else /* !CONFIG_KGDB */
-static inline void uv_call_kgdb_kdb(int cpu, struct pt_regs *regs, int master)
-{
-	pr_err("UV: NMI error: KGDB is not enabled in this kernel\n");
-}
-#endif /* !CONFIG_KGDB */
-
 /*
  * UV NMI handler
  */
@@ -974,10 +902,6 @@ static int uv_handle_nmi(unsigned int reason, struct pt_regs *regs)
 	case nmi_act_dump:
 		uv_nmi_dump_state(cpu, regs, master);
 		break;
-	case nmi_act_kdb:
-	case nmi_act_kgdb:
-		uv_call_kgdb_kdb(cpu, regs, master);
-		break;
 	default:
 		if (master)
 			pr_alert("UV: unknown NMI action: %d\n", uv_nmi_action);

Re: [PATCH] x86: Drop KGDB support

[H. Peter Anvin]

On October 28, 2026 5:21:24 AM PDT, Peter Zijlstra <peterz@infradead.org> wrote:
>
>KGDB does some horrible things, and with everybody having access to
>virtualization these days, there is really no reason to use it over
>Qemu's gdb-server.
>
>Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>---
> arch/x86/Kconfig                     |   2 -
> arch/x86/include/asm/kgdb.h          |  92 ----
> arch/x86/include/asm/text-patching.h |   1 -
> arch/x86/kernel/Makefile             |   1 -
> arch/x86/kernel/alternative.c        |  50 +--
> arch/x86/kernel/cpu/common.c         |  16 -
> arch/x86/kernel/early_printk.c       |   8 -
> arch/x86/kernel/kgdb.c               | 785 -----------------------------------
> arch/x86/kernel/kprobes/core.c       |  10 -
> arch/x86/kernel/kprobes/opt.c        |  11 +-
> arch/x86/kernel/traps.c              |  10 +-
> arch/x86/platform/uv/uv_nmi.c        |  76 ----
> 12 files changed, 13 insertions(+), 1049 deletions(-)
>
>diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>index a5e29ffd5ddc..627553e8496f 100644
>--- a/arch/x86/Kconfig
>+++ b/arch/x86/Kconfig
>@@ -82,7 +82,6 @@ config X86
> 	select ARCH_HAS_DELAY_TIMER
> 	select ARCH_HAS_DEVMEM_IS_ALLOWED
> 	select ARCH_HAS_DMA_OPS			if GART_IOMMU || XEN
>-	select ARCH_HAS_EARLY_DEBUG		if KGDB
> 	select ARCH_HAS_ELF_RANDOMIZE
> 	select ARCH_HAS_EXECMEM_ROX		if X86_64 && STRICT_MODULE_RWX
> 	select ARCH_HAS_FAST_MULTIPLIER
>@@ -198,7 +197,6 @@ config X86
> 	select HAVE_ARCH_KASAN_VMALLOC		if X86_64
> 	select HAVE_ARCH_KFENCE
> 	select HAVE_ARCH_KMSAN			if X86_64
>-	select HAVE_ARCH_KGDB
> 	select HAVE_ARCH_KSTACK_ERASE
> 	select HAVE_ARCH_MMAP_RND_BITS		if MMU
> 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS	if MMU && COMPAT
>diff --git a/arch/x86/include/asm/kgdb.h b/arch/x86/include/asm/kgdb.h
>deleted file mode 100644
>index aacaf2502bd2..000000000000
>--- a/arch/x86/include/asm/kgdb.h
>+++ /dev/null
>@@ -1,92 +0,0 @@
>-/* SPDX-License-Identifier: GPL-2.0 */
>-#ifndef _ASM_X86_KGDB_H
>-#define _ASM_X86_KGDB_H
>-
>-/*
>- * Copyright (C) 2001-2004 Amit S. Kale
>- * Copyright (C) 2008 Wind River Systems, Inc.
>- */
>-
>-#include <asm/ptrace.h>
>-
>-/*
>- * BUFMAX defines the maximum number of characters in inbound/outbound
>- * buffers at least NUMREGBYTES*2 are needed for register packets
>- * Longer buffer is needed to list all threads
>- */
>-#define BUFMAX			1024
>-
>-/*
>- *  Note that this register image is in a different order than
>- *  the register image that Linux produces at interrupt time.
>- *
>- *  Linux's register image is defined by struct pt_regs in ptrace.h.
>- *  Just why GDB uses a different order is a historical mystery.
>- */
>-#ifdef CONFIG_X86_32
>-enum regnames {
>-	GDB_AX,			/* 0 */
>-	GDB_CX,			/* 1 */
>-	GDB_DX,			/* 2 */
>-	GDB_BX,			/* 3 */
>-	GDB_SP,			/* 4 */
>-	GDB_BP,			/* 5 */
>-	GDB_SI,			/* 6 */
>-	GDB_DI,			/* 7 */
>-	GDB_PC,			/* 8 also known as eip */
>-	GDB_PS,			/* 9 also known as eflags */
>-	GDB_CS,			/* 10 */
>-	GDB_SS,			/* 11 */
>-	GDB_DS,			/* 12 */
>-	GDB_ES,			/* 13 */
>-	GDB_FS,			/* 14 */
>-	GDB_GS,			/* 15 */
>-};
>-#define GDB_ORIG_AX		41
>-#define DBG_MAX_REG_NUM		16
>-#define NUMREGBYTES		((GDB_GS+1)*4)
>-#else /* ! CONFIG_X86_32 */
>-enum regnames {
>-	GDB_AX,			/* 0 */
>-	GDB_BX,			/* 1 */
>-	GDB_CX,			/* 2 */
>-	GDB_DX,			/* 3 */
>-	GDB_SI,			/* 4 */
>-	GDB_DI,			/* 5 */
>-	GDB_BP,			/* 6 */
>-	GDB_SP,			/* 7 */
>-	GDB_R8,			/* 8 */
>-	GDB_R9,			/* 9 */
>-	GDB_R10,		/* 10 */
>-	GDB_R11,		/* 11 */
>-	GDB_R12,		/* 12 */
>-	GDB_R13,		/* 13 */
>-	GDB_R14,		/* 14 */
>-	GDB_R15,		/* 15 */
>-	GDB_PC,			/* 16 */
>-	GDB_PS,			/* 17 */
>-	GDB_CS,			/* 18 */
>-	GDB_SS,			/* 19 */
>-	GDB_DS,			/* 20 */
>-	GDB_ES,			/* 21 */
>-	GDB_FS,			/* 22 */
>-	GDB_GS,			/* 23 */
>-};
>-#define GDB_ORIG_AX		57
>-#define DBG_MAX_REG_NUM		24
>-/* 17 64 bit regs and 5 32 bit regs */
>-#define NUMREGBYTES		((17 * 8) + (5 * 4))
>-#endif /* ! CONFIG_X86_32 */
>-
>-static inline void arch_kgdb_breakpoint(void)
>-{
>-	asm("   int $3");
>-}
>-#define BREAK_INSTR_SIZE	1
>-#define CACHE_FLUSH_IS_SAFE	1
>-#define GDB_ADJUSTS_BREAK_OFFSET
>-
>-extern int kgdb_ll_trap(int cmd, const char *str,
>-			struct pt_regs *regs, long err, int trap, int sig);
>-
>-#endif /* _ASM_X86_KGDB_H */
>diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
>index ea09381070e8..a1d284560ef8 100644
>--- a/arch/x86/include/asm/text-patching.h
>+++ b/arch/x86/include/asm/text-patching.h
>@@ -33,7 +33,6 @@ extern void text_poke_apply_relocation(u8 *buf, const u8 * const instr, size_t i
>  */
> extern void *text_poke(void *addr, const void *opcode, size_t len);
> extern void smp_text_poke_sync_each_cpu(void);
>-extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
> extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
> #define text_poke_copy text_poke_copy
> extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok);
>diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
>index 31f46fd00527..1a16af34dee3 100644
>--- a/arch/x86/kernel/Makefile
>+++ b/arch/x86/kernel/Makefile
>@@ -128,7 +128,6 @@ obj-$(CONFIG_CRASH_DUMP)	+= crash_dump_$(BITS).o crash.o
> obj-y				+= kprobes/
> obj-$(CONFIG_MODULES)		+= module.o
> obj-$(CONFIG_X86_32)		+= doublefault_32.o
>-obj-$(CONFIG_KGDB)		+= kgdb.o
> obj-$(CONFIG_VM86)		+= vm86_32.o
> obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
> 
>diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
>index efbc11f8c336..d8add52ff923 100644
>--- a/arch/x86/kernel/alternative.c
>+++ b/arch/x86/kernel/alternative.c
>@@ -7,7 +7,6 @@
> #include <linux/memory.h>
> #include <linux/execmem.h>
> #include <linux/cleanup.h>
>-#include <linux/kgdb.h>
> #include <linux/mmap_lock.h>
> 
> #include <asm/text-patching.h>
>@@ -2393,25 +2392,17 @@ static void __poke_vmalloc_pages(struct page **pages, void *addr,
> static void poke_vmalloc_pages(struct page **pages, void *addr,
> 			       bool cross_page_boundary)
> {
>-	if (in_dbg_master()) {
>-		/*
>-		 * If called from kgdb cannot sleep, but all other CPUs stopped
>-		 * anyway so safe to proceed without locks
>-		 */
>-		__poke_vmalloc_pages(pages, addr, cross_page_boundary);
>-	} else {
>-		/*
>-		 * execmem ROX ranges are shared between modules and can be
>-		 * collapsed to huge PMD entries, and this collapse can happen
>-		 * concurrently with a racing set_memory_rox().
>-		 *
>-		 * Prevent vmalloc_to_page() from racing by acquiring an
>-		 * init_mm read lock which pairs with the init_mm write lock in
>-		 * cpa_collapse_large_pages().
>-		 */
>-		guard(mmap_read_lock)(&init_mm);
>-		__poke_vmalloc_pages(pages, addr, cross_page_boundary);
>-	}
>+	/*
>+	 * execmem ROX ranges are shared between modules and can be
>+	 * collapsed to huge PMD entries, and this collapse can happen
>+	 * concurrently with a racing set_memory_rox().
>+	 *
>+	 * Prevent vmalloc_to_page() from racing by acquiring an
>+	 * init_mm read lock which pairs with the init_mm write lock in
>+	 * cpa_collapse_large_pages().
>+	 */
>+	guard(mmap_read_lock)(&init_mm);
>+	__poke_vmalloc_pages(pages, addr, cross_page_boundary);
> }
> 
> static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len)
>@@ -2541,25 +2532,6 @@ void *text_poke(void *addr, const void *opcode, size_t len)
> 	return __text_poke(text_poke_memcpy, addr, opcode, len);
> }
> 
>-/**
>- * text_poke_kgdb - Update instructions on a live kernel by kgdb
>- * @addr: address to modify
>- * @opcode: source of the copy
>- * @len: length to copy
>- *
>- * Only atomic text poke/set should be allowed when not doing early patching.
>- * It means the size must be writable atomically and the address must be aligned
>- * in a way that permits an atomic write. It also makes sure we fit on a single
>- * page.
>- *
>- * Context: should only be used by kgdb, which ensures no other core is running,
>- *	    despite the fact it does not hold the text_mutex.
>- */
>-void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
>-{
>-	return __text_poke(text_poke_memcpy, addr, opcode, len);
>-}
>-
> void *text_poke_copy_locked(void *addr, const void *opcode, size_t len,
> 			    bool core_ok)
> {
>diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
>index 9bd50c68cd7e..8a4aabcd5d60 100644
>--- a/arch/x86/kernel/cpu/common.c
>+++ b/arch/x86/kernel/cpu/common.c
>@@ -18,7 +18,6 @@
> #include <linux/sched/smt.h>
> #include <linux/init.h>
> #include <linux/kprobes.h>
>-#include <linux/kgdb.h>
> #include <linux/mem_encrypt.h>
> #include <linux/smp.h>
> #include <linux/cpu.h>
>@@ -2340,20 +2339,6 @@ static void initialize_debug_regs(void)
> 	set_debugreg(0, 0);
> }
> 
>-#ifdef CONFIG_KGDB
>-/*
>- * Restore debug regs if using kgdbwait and you have a kernel debugger
>- * connection established.
>- */
>-static void dbg_restore_debug_regs(void)
>-{
>-	if (unlikely(kgdb_connected && arch_kgdb_ops.correct_hw_break))
>-		arch_kgdb_ops.correct_hw_break();
>-}
>-#else /* ! CONFIG_KGDB */
>-#define dbg_restore_debug_regs()
>-#endif /* ! CONFIG_KGDB */
>-
> static inline void setup_getcpu(int cpu)
> {
> 	unsigned long cpudata = vdso_encode_cpunode(cpu, early_cpu_to_node(cpu));
>@@ -2511,7 +2496,6 @@ void cpu_init(void)
> 	load_mm_ldt(&init_mm);
> 
> 	initialize_debug_regs();
>-	dbg_restore_debug_regs();
> 
> 	doublefault_init_cpu_tss();
> 
>diff --git a/arch/x86/kernel/early_printk.c b/arch/x86/kernel/early_printk.c
>index cba75306e5b6..ad7534771bcf 100644
>--- a/arch/x86/kernel/early_printk.c
>+++ b/arch/x86/kernel/early_printk.c
>@@ -46,14 +46,6 @@ static void early_vga_write(struct console *con, const char *str, unsigned n)
> 				writew(0x720, VGABASE + 2*(max_xpos*j + i));
> 			current_ypos = max_ypos-1;
> 		}
>-#ifdef CONFIG_KGDB_KDB
>-		if (c == '\b') {
>-			if (current_xpos > 0)
>-				current_xpos--;
>-		} else if (c == '\r') {
>-			current_xpos = 0;
>-		} else
>-#endif
> 		if (c == '\n') {
> 			current_xpos = 0;
> 			current_ypos++;
>diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
>deleted file mode 100644
>index 96af1242454e..000000000000
>--- a/arch/x86/kernel/kgdb.c
>+++ /dev/null
>@@ -1,785 +0,0 @@
>-// SPDX-License-Identifier: GPL-2.0-or-later
>-/*
>- */
>-
>-/*
>- * Copyright (C) 2004 Amit S. Kale <amitkale@linsyssoft.com>
>- * Copyright (C) 2000-2001 VERITAS Software Corporation.
>- * Copyright (C) 2002 Andi Kleen, SuSE Labs
>- * Copyright (C) 2004 LinSysSoft Technologies Pvt. Ltd.
>- * Copyright (C) 2007 MontaVista Software, Inc.
>- * Copyright (C) 2007-2008 Jason Wessel, Wind River Systems, Inc.
>- */
>-/****************************************************************************
>- *  Contributor:     Lake Stevens Instrument Division$
>- *  Written by:      Glenn Engel $
>- *  Updated by:	     Amit Kale<akale@veritas.com>
>- *  Updated by:	     Tom Rini <trini@kernel.crashing.org>
>- *  Updated by:	     Jason Wessel <jason.wessel@windriver.com>
>- *  Modified for 386 by Jim Kingdon, Cygnus Support.
>- *  Original kgdb, compatibility with 2.1.xx kernel by
>- *  David Grothe <dave@gcom.com>
>- *  Integrated into 2.2.5 kernel by Tigran Aivazian <tigran@sco.com>
>- *  X86_64 changes from Andi Kleen's patch merged by Jim Houston
>- */
>-#include <linux/spinlock.h>
>-#include <linux/kdebug.h>
>-#include <linux/string.h>
>-#include <linux/kernel.h>
>-#include <linux/ptrace.h>
>-#include <linux/sched.h>
>-#include <linux/delay.h>
>-#include <linux/kgdb.h>
>-#include <linux/smp.h>
>-#include <linux/nmi.h>
>-#include <linux/hw_breakpoint.h>
>-#include <linux/uaccess.h>
>-#include <linux/memory.h>
>-
>-#include <asm/text-patching.h>
>-#include <asm/debugreg.h>
>-#include <asm/apicdef.h>
>-#include <asm/apic.h>
>-#include <asm/nmi.h>
>-#include <asm/switch_to.h>
>-
>-struct dbg_reg_def_t dbg_reg_def[DBG_MAX_REG_NUM] =
>-{
>-#ifdef CONFIG_X86_32
>-	{ "ax", 4, offsetof(struct pt_regs, ax) },
>-	{ "cx", 4, offsetof(struct pt_regs, cx) },
>-	{ "dx", 4, offsetof(struct pt_regs, dx) },
>-	{ "bx", 4, offsetof(struct pt_regs, bx) },
>-	{ "sp", 4, offsetof(struct pt_regs, sp) },
>-	{ "bp", 4, offsetof(struct pt_regs, bp) },
>-	{ "si", 4, offsetof(struct pt_regs, si) },
>-	{ "di", 4, offsetof(struct pt_regs, di) },
>-	{ "ip", 4, offsetof(struct pt_regs, ip) },
>-	{ "flags", 4, offsetof(struct pt_regs, flags) },
>-	{ "cs", 4, offsetof(struct pt_regs, cs) },
>-	{ "ss", 4, offsetof(struct pt_regs, ss) },
>-	{ "ds", 4, offsetof(struct pt_regs, ds) },
>-	{ "es", 4, offsetof(struct pt_regs, es) },
>-#else
>-	{ "ax", 8, offsetof(struct pt_regs, ax) },
>-	{ "bx", 8, offsetof(struct pt_regs, bx) },
>-	{ "cx", 8, offsetof(struct pt_regs, cx) },
>-	{ "dx", 8, offsetof(struct pt_regs, dx) },
>-	{ "si", 8, offsetof(struct pt_regs, si) },
>-	{ "di", 8, offsetof(struct pt_regs, di) },
>-	{ "bp", 8, offsetof(struct pt_regs, bp) },
>-	{ "sp", 8, offsetof(struct pt_regs, sp) },
>-	{ "r8", 8, offsetof(struct pt_regs, r8) },
>-	{ "r9", 8, offsetof(struct pt_regs, r9) },
>-	{ "r10", 8, offsetof(struct pt_regs, r10) },
>-	{ "r11", 8, offsetof(struct pt_regs, r11) },
>-	{ "r12", 8, offsetof(struct pt_regs, r12) },
>-	{ "r13", 8, offsetof(struct pt_regs, r13) },
>-	{ "r14", 8, offsetof(struct pt_regs, r14) },
>-	{ "r15", 8, offsetof(struct pt_regs, r15) },
>-	{ "ip", 8, offsetof(struct pt_regs, ip) },
>-	{ "flags", 4, offsetof(struct pt_regs, flags) },
>-	{ "cs", 4, offsetof(struct pt_regs, cs) },
>-	{ "ss", 4, offsetof(struct pt_regs, ss) },
>-	{ "ds", 4, -1 },
>-	{ "es", 4, -1 },
>-#endif
>-	{ "fs", 4, -1 },
>-	{ "gs", 4, -1 },
>-};
>-
>-int dbg_set_reg(int regno, void *mem, struct pt_regs *regs)
>-{
>-	if (
>-#ifdef CONFIG_X86_32
>-	    regno == GDB_SS || regno == GDB_FS || regno == GDB_GS ||
>-#endif
>-	    regno == GDB_SP || regno == GDB_ORIG_AX)
>-		return 0;
>-
>-	if (dbg_reg_def[regno].offset != -1)
>-		memcpy((void *)regs + dbg_reg_def[regno].offset, mem,
>-		       dbg_reg_def[regno].size);
>-	return 0;
>-}
>-
>-char *dbg_get_reg(int regno, void *mem, struct pt_regs *regs)
>-{
>-	if (regno == GDB_ORIG_AX) {
>-		memcpy(mem, &regs->orig_ax, sizeof(regs->orig_ax));
>-		return "orig_ax";
>-	}
>-	if (regno >= DBG_MAX_REG_NUM || regno < 0)
>-		return NULL;
>-
>-	if (dbg_reg_def[regno].offset != -1)
>-		memcpy(mem, (void *)regs + dbg_reg_def[regno].offset,
>-		       dbg_reg_def[regno].size);
>-
>-#ifdef CONFIG_X86_32
>-	switch (regno) {
>-	case GDB_GS:
>-	case GDB_FS:
>-		*(unsigned long *)mem = 0xFFFF;
>-		break;
>-	}
>-#endif
>-	return dbg_reg_def[regno].name;
>-}
>-
>-/**
>- *	sleeping_thread_to_gdb_regs - Convert ptrace regs to GDB regs
>- *	@gdb_regs: A pointer to hold the registers in the order GDB wants.
>- *	@p: The &struct task_struct of the desired process.
>- *
>- *	Convert the register values of the sleeping process in @p to
>- *	the format that GDB expects.
>- *	This function is called when kgdb does not have access to the
>- *	&struct pt_regs and therefore it should fill the gdb registers
>- *	@gdb_regs with what has	been saved in &struct thread_struct
>- *	thread field during switch_to.
>- */
>-void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct task_struct *p)
>-{
>-#ifndef CONFIG_X86_32
>-	u32 *gdb_regs32 = (u32 *)gdb_regs;
>-#endif
>-	gdb_regs[GDB_AX]	= 0;
>-	gdb_regs[GDB_BX]	= 0;
>-	gdb_regs[GDB_CX]	= 0;
>-	gdb_regs[GDB_DX]	= 0;
>-	gdb_regs[GDB_SI]	= 0;
>-	gdb_regs[GDB_DI]	= 0;
>-	gdb_regs[GDB_BP]	= ((struct inactive_task_frame *)p->thread.sp)->bp;
>-#ifdef CONFIG_X86_32
>-	gdb_regs[GDB_DS]	= __KERNEL_DS;
>-	gdb_regs[GDB_ES]	= __KERNEL_DS;
>-	gdb_regs[GDB_PS]	= 0;
>-	gdb_regs[GDB_CS]	= __KERNEL_CS;
>-	gdb_regs[GDB_SS]	= __KERNEL_DS;
>-	gdb_regs[GDB_FS]	= 0xFFFF;
>-	gdb_regs[GDB_GS]	= 0xFFFF;
>-#else
>-	gdb_regs32[GDB_PS]	= 0;
>-	gdb_regs32[GDB_CS]	= __KERNEL_CS;
>-	gdb_regs32[GDB_SS]	= __KERNEL_DS;
>-	gdb_regs[GDB_R8]	= 0;
>-	gdb_regs[GDB_R9]	= 0;
>-	gdb_regs[GDB_R10]	= 0;
>-	gdb_regs[GDB_R11]	= 0;
>-	gdb_regs[GDB_R12]	= 0;
>-	gdb_regs[GDB_R13]	= 0;
>-	gdb_regs[GDB_R14]	= 0;
>-	gdb_regs[GDB_R15]	= 0;
>-#endif
>-	gdb_regs[GDB_PC]	= 0;
>-	gdb_regs[GDB_SP]	= p->thread.sp;
>-}
>-
>-static struct hw_breakpoint {
>-	unsigned		enabled;
>-	unsigned long		addr;
>-	int			len;
>-	int			type;
>-	struct perf_event	* __percpu *pev;
>-} breakinfo[HBP_NUM];
>-
>-static unsigned long early_dr7;
>-
>-static void kgdb_correct_hw_break(void)
>-{
>-	int breakno;
>-
>-	for (breakno = 0; breakno < HBP_NUM; breakno++) {
>-		struct perf_event *bp;
>-		struct arch_hw_breakpoint *info;
>-		int val;
>-		int cpu = raw_smp_processor_id();
>-		if (!breakinfo[breakno].enabled)
>-			continue;
>-		if (dbg_is_early) {
>-			set_debugreg(breakinfo[breakno].addr, breakno);
>-			early_dr7 |= encode_dr7(breakno,
>-						breakinfo[breakno].len,
>-						breakinfo[breakno].type);
>-			set_debugreg(early_dr7, 7);
>-			continue;
>-		}
>-		bp = *per_cpu_ptr(breakinfo[breakno].pev, cpu);
>-		info = counter_arch_bp(bp);
>-		if (bp->attr.disabled != 1)
>-			continue;
>-		bp->attr.bp_addr = breakinfo[breakno].addr;
>-		bp->attr.bp_len = breakinfo[breakno].len;
>-		bp->attr.bp_type = breakinfo[breakno].type;
>-		info->address = breakinfo[breakno].addr;
>-		info->len = breakinfo[breakno].len;
>-		info->type = breakinfo[breakno].type;
>-		val = arch_install_hw_breakpoint(bp);
>-		if (!val)
>-			bp->attr.disabled = 0;
>-	}
>-	if (!dbg_is_early)
>-		hw_breakpoint_restore();
>-}
>-
>-static int hw_break_reserve_slot(int breakno)
>-{
>-	int cpu;
>-	int cnt = 0;
>-	struct perf_event **pevent;
>-
>-	if (dbg_is_early)
>-		return 0;
>-
>-	for_each_online_cpu(cpu) {
>-		cnt++;
>-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
>-		if (dbg_reserve_bp_slot(*pevent))
>-			goto fail;
>-	}
>-
>-	return 0;
>-
>-fail:
>-	for_each_online_cpu(cpu) {
>-		cnt--;
>-		if (!cnt)
>-			break;
>-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
>-		dbg_release_bp_slot(*pevent);
>-	}
>-	return -1;
>-}
>-
>-static int hw_break_release_slot(int breakno)
>-{
>-	struct perf_event **pevent;
>-	int cpu;
>-
>-	if (dbg_is_early)
>-		return 0;
>-
>-	for_each_online_cpu(cpu) {
>-		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
>-		if (dbg_release_bp_slot(*pevent))
>-			/*
>-			 * The debugger is responsible for handing the retry on
>-			 * remove failure.
>-			 */
>-			return -1;
>-	}
>-	return 0;
>-}
>-
>-static int
>-kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
>-{
>-	int i;
>-
>-	for (i = 0; i < HBP_NUM; i++)
>-		if (breakinfo[i].addr == addr && breakinfo[i].enabled)
>-			break;
>-	if (i == HBP_NUM)
>-		return -1;
>-
>-	if (hw_break_release_slot(i)) {
>-		printk(KERN_ERR "Cannot remove hw breakpoint at %lx\n", addr);
>-		return -1;
>-	}
>-	breakinfo[i].enabled = 0;
>-
>-	return 0;
>-}
>-
>-static void kgdb_remove_all_hw_break(void)
>-{
>-	int i;
>-	int cpu = raw_smp_processor_id();
>-	struct perf_event *bp;
>-
>-	for (i = 0; i < HBP_NUM; i++) {
>-		if (!breakinfo[i].enabled)
>-			continue;
>-		bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
>-		if (!bp->attr.disabled) {
>-			arch_uninstall_hw_breakpoint(bp);
>-			bp->attr.disabled = 1;
>-			continue;
>-		}
>-		if (dbg_is_early)
>-			early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
>-						 breakinfo[i].type);
>-		else if (hw_break_release_slot(i))
>-			printk(KERN_ERR "KGDB: hw bpt remove failed %lx\n",
>-			       breakinfo[i].addr);
>-		breakinfo[i].enabled = 0;
>-	}
>-}
>-
>-static int
>-kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
>-{
>-	int i;
>-
>-	for (i = 0; i < HBP_NUM; i++)
>-		if (!breakinfo[i].enabled)
>-			break;
>-	if (i == HBP_NUM)
>-		return -1;
>-
>-	switch (bptype) {
>-	case BP_HARDWARE_BREAKPOINT:
>-		len = 1;
>-		breakinfo[i].type = X86_BREAKPOINT_EXECUTE;
>-		break;
>-	case BP_WRITE_WATCHPOINT:
>-		breakinfo[i].type = X86_BREAKPOINT_WRITE;
>-		break;
>-	case BP_ACCESS_WATCHPOINT:
>-		breakinfo[i].type = X86_BREAKPOINT_RW;
>-		break;
>-	default:
>-		return -1;
>-	}
>-	switch (len) {
>-	case 1:
>-		breakinfo[i].len = X86_BREAKPOINT_LEN_1;
>-		break;
>-	case 2:
>-		breakinfo[i].len = X86_BREAKPOINT_LEN_2;
>-		break;
>-	case 4:
>-		breakinfo[i].len = X86_BREAKPOINT_LEN_4;
>-		break;
>-#ifdef CONFIG_X86_64
>-	case 8:
>-		breakinfo[i].len = X86_BREAKPOINT_LEN_8;
>-		break;
>-#endif
>-	default:
>-		return -1;
>-	}
>-	breakinfo[i].addr = addr;
>-	if (hw_break_reserve_slot(i)) {
>-		breakinfo[i].addr = 0;
>-		return -1;
>-	}
>-	breakinfo[i].enabled = 1;
>-
>-	return 0;
>-}
>-
>-/**
>- *	kgdb_disable_hw_debug - Disable hardware debugging while we in kgdb.
>- *	@regs: Current &struct pt_regs.
>- *
>- *	This function will be called if the particular architecture must
>- *	disable hardware debugging while it is processing gdb packets or
>- *	handling exception.
>- */
>-static void kgdb_disable_hw_debug(struct pt_regs *regs)
>-{
>-	int i;
>-	int cpu = raw_smp_processor_id();
>-	struct perf_event *bp;
>-
>-	/* Disable hardware debugging while we are in kgdb: */
>-	set_debugreg(DR7_FIXED_1, 7);
>-	for (i = 0; i < HBP_NUM; i++) {
>-		if (!breakinfo[i].enabled)
>-			continue;
>-		if (dbg_is_early) {
>-			early_dr7 &= ~encode_dr7(i, breakinfo[i].len,
>-						 breakinfo[i].type);
>-			continue;
>-		}
>-		bp = *per_cpu_ptr(breakinfo[i].pev, cpu);
>-		if (bp->attr.disabled == 1)
>-			continue;
>-		arch_uninstall_hw_breakpoint(bp);
>-		bp->attr.disabled = 1;
>-	}
>-}
>-
>-#ifdef CONFIG_SMP
>-/**
>- *	kgdb_roundup_cpus - Get other CPUs into a holding pattern
>- *
>- *	On SMP systems, we need to get the attention of the other CPUs
>- *	and get them into a known state.  This should do what is needed
>- *	to get the other CPUs to call kgdb_handle_exception().  Note that
>- *	on some arches, the NMI approach is not used for rounding up all
>- *	the CPUs.  For example, in case of MIPS, smp_call_function() is
>- *	used to roundup CPUs.
>- *
>- *	On non-SMP systems, this is not called.
>- */
>-void kgdb_roundup_cpus(void)
>-{
>-	apic_send_IPI_allbutself(NMI_VECTOR);
>-}
>-#endif
>-
>-/**
>- *	kgdb_arch_handle_exception - Handle architecture specific GDB packets.
>- *	@e_vector: The error vector of the exception that happened.
>- *	@signo: The signal number of the exception that happened.
>- *	@err_code: The error code of the exception that happened.
>- *	@remcomInBuffer: The buffer of the packet we have read.
>- *	@remcomOutBuffer: The buffer of %BUFMAX bytes to write a packet into.
>- *	@linux_regs: The &struct pt_regs of the current process.
>- *
>- *	This function MUST handle the 'c' and 's' command packets,
>- *	as well packets to set / remove a hardware breakpoint, if used.
>- *	If there are additional packets which the hardware needs to handle,
>- *	they are handled here.  The code should return -1 if it wants to
>- *	process more packets, and a %0 or %1 if it wants to exit from the
>- *	kgdb callback.
>- */
>-int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
>-			       char *remcomInBuffer, char *remcomOutBuffer,
>-			       struct pt_regs *linux_regs)
>-{
>-	unsigned long addr;
>-	char *ptr;
>-
>-	switch (remcomInBuffer[0]) {
>-	case 'c':
>-	case 's':
>-		/* try to read optional parameter, pc unchanged if no parm */
>-		ptr = &remcomInBuffer[1];
>-		if (kgdb_hex2long(&ptr, &addr))
>-			linux_regs->ip = addr;
>-		fallthrough;
>-	case 'D':
>-	case 'k':
>-		/* clear the trace bit */
>-		linux_regs->flags &= ~X86_EFLAGS_TF;
>-		atomic_set(&kgdb_cpu_doing_single_step, -1);
>-
>-		/* set the trace bit if we're stepping */
>-		if (remcomInBuffer[0] == 's') {
>-			linux_regs->flags |= X86_EFLAGS_TF;
>-			atomic_set(&kgdb_cpu_doing_single_step,
>-				   raw_smp_processor_id());
>-		}
>-
>-		return 0;
>-	}
>-
>-	/* this means that we do not want to exit from the handler: */
>-	return -1;
>-}
>-
>-static inline int
>-single_step_cont(struct pt_regs *regs, struct die_args *args)
>-{
>-	/*
>-	 * Single step exception from kernel space to user space so
>-	 * eat the exception and continue the process:
>-	 */
>-	printk(KERN_ERR "KGDB: trap/step from kernel to user space, "
>-			"resuming...\n");
>-	kgdb_arch_handle_exception(args->trapnr, args->signr,
>-				   args->err, "c", "", regs);
>-	/*
>-	 * Reset the BS bit in dr6 (pointed by args->err) to
>-	 * denote completion of processing
>-	 */
>-	(*(unsigned long *)ERR_PTR(args->err)) &= ~DR_STEP;
>-
>-	return NOTIFY_STOP;
>-}
>-
>-static DECLARE_BITMAP(was_in_debug_nmi, NR_CPUS);
>-
>-static int kgdb_nmi_handler(unsigned int cmd, struct pt_regs *regs)
>-{
>-	int cpu;
>-
>-	switch (cmd) {
>-	case NMI_LOCAL:
>-		if (atomic_read(&kgdb_active) != -1) {
>-			/* KGDB CPU roundup */
>-			cpu = raw_smp_processor_id();
>-			kgdb_nmicallback(cpu, regs);
>-			set_bit(cpu, was_in_debug_nmi);
>-			touch_nmi_watchdog();
>-
>-			return NMI_HANDLED;
>-		}
>-		break;
>-
>-	case NMI_UNKNOWN:
>-		cpu = raw_smp_processor_id();
>-
>-		if (__test_and_clear_bit(cpu, was_in_debug_nmi))
>-			return NMI_HANDLED;
>-
>-		break;
>-	default:
>-		/* do nothing */
>-		break;
>-	}
>-	return NMI_DONE;
>-}
>-
>-static int __kgdb_notify(struct die_args *args, unsigned long cmd)
>-{
>-	struct pt_regs *regs = args->regs;
>-
>-	switch (cmd) {
>-	case DIE_DEBUG:
>-		if (atomic_read(&kgdb_cpu_doing_single_step) != -1) {
>-			if (user_mode(regs))
>-				return single_step_cont(regs, args);
>-			break;
>-		} else if (test_thread_flag(TIF_SINGLESTEP))
>-			/* This means a user thread is single stepping
>-			 * a system call which should be ignored
>-			 */
>-			return NOTIFY_DONE;
>-		fallthrough;
>-	default:
>-		if (user_mode(regs))
>-			return NOTIFY_DONE;
>-	}
>-
>-	if (kgdb_handle_exception(args->trapnr, args->signr, cmd, regs))
>-		return NOTIFY_DONE;
>-
>-	/* Must touch watchdog before return to normal operation */
>-	touch_nmi_watchdog();
>-	return NOTIFY_STOP;
>-}
>-
>-int kgdb_ll_trap(int cmd, const char *str,
>-		 struct pt_regs *regs, long err, int trap, int sig)
>-{
>-	struct die_args args = {
>-		.regs	= regs,
>-		.str	= str,
>-		.err	= err,
>-		.trapnr	= trap,
>-		.signr	= sig,
>-
>-	};
>-
>-	if (!kgdb_io_module_registered)
>-		return NOTIFY_DONE;
>-
>-	return __kgdb_notify(&args, cmd);
>-}
>-
>-static int
>-kgdb_notify(struct notifier_block *self, unsigned long cmd, void *ptr)
>-{
>-	unsigned long flags;
>-	int ret;
>-
>-	local_irq_save(flags);
>-	ret = __kgdb_notify(ptr, cmd);
>-	local_irq_restore(flags);
>-
>-	return ret;
>-}
>-
>-static struct notifier_block kgdb_notifier = {
>-	.notifier_call	= kgdb_notify,
>-};
>-
>-/**
>- *	kgdb_arch_init - Perform any architecture specific initialization.
>- *
>- *	This function will handle the initialization of any architecture
>- *	specific callbacks.
>- */
>-int kgdb_arch_init(void)
>-{
>-	int retval;
>-
>-	retval = register_die_notifier(&kgdb_notifier);
>-	if (retval)
>-		goto out;
>-
>-	retval = register_nmi_handler(NMI_LOCAL, kgdb_nmi_handler,
>-					0, "kgdb");
>-	if (retval)
>-		goto out1;
>-
>-	retval = register_nmi_handler(NMI_UNKNOWN, kgdb_nmi_handler,
>-					0, "kgdb");
>-
>-	if (retval)
>-		goto out2;
>-
>-	return retval;
>-
>-out2:
>-	unregister_nmi_handler(NMI_LOCAL, "kgdb");
>-out1:
>-	unregister_die_notifier(&kgdb_notifier);
>-out:
>-	return retval;
>-}
>-
>-static void kgdb_hw_overflow_handler(struct perf_event *event,
>-		struct perf_sample_data *data, struct pt_regs *regs)
>-{
>-	struct task_struct *tsk = current;
>-	int i;
>-
>-	for (i = 0; i < 4; i++) {
>-		if (breakinfo[i].enabled)
>-			tsk->thread.virtual_dr6 |= (DR_TRAP0 << i);
>-	}
>-}
>-
>-void kgdb_arch_late(void)
>-{
>-	int i, cpu;
>-	struct perf_event_attr attr;
>-	struct perf_event **pevent;
>-
>-	/*
>-	 * Pre-allocate the hw breakpoint instructions in the non-atomic
>-	 * portion of kgdb because this operation requires mutexs to
>-	 * complete.
>-	 */
>-	hw_breakpoint_init(&attr);
>-	attr.bp_addr = (unsigned long)kgdb_arch_init;
>-	attr.bp_len = HW_BREAKPOINT_LEN_1;
>-	attr.bp_type = HW_BREAKPOINT_W;
>-	attr.disabled = 1;
>-	for (i = 0; i < HBP_NUM; i++) {
>-		if (breakinfo[i].pev)
>-			continue;
>-		breakinfo[i].pev = register_wide_hw_breakpoint(&attr, NULL, NULL);
>-		if (IS_ERR_PCPU(breakinfo[i].pev)) {
>-			printk(KERN_ERR "kgdb: Could not allocate hw"
>-			       "breakpoints\nDisabling the kernel debugger\n");
>-			breakinfo[i].pev = NULL;
>-			kgdb_arch_exit();
>-			return;
>-		}
>-		for_each_online_cpu(cpu) {
>-			pevent = per_cpu_ptr(breakinfo[i].pev, cpu);
>-			pevent[0]->hw.sample_period = 1;
>-			pevent[0]->overflow_handler = kgdb_hw_overflow_handler;
>-			if (pevent[0]->destroy != NULL) {
>-				pevent[0]->destroy = NULL;
>-				release_bp_slot(*pevent);
>-			}
>-		}
>-	}
>-}
>-
>-/**
>- *	kgdb_arch_exit - Perform any architecture specific uninitalization.
>- *
>- *	This function will handle the uninitalization of any architecture
>- *	specific callbacks, for dynamic registration and unregistration.
>- */
>-void kgdb_arch_exit(void)
>-{
>-	int i;
>-	for (i = 0; i < 4; i++) {
>-		if (breakinfo[i].pev) {
>-			unregister_wide_hw_breakpoint(breakinfo[i].pev);
>-			breakinfo[i].pev = NULL;
>-		}
>-	}
>-	unregister_nmi_handler(NMI_UNKNOWN, "kgdb");
>-	unregister_nmi_handler(NMI_LOCAL, "kgdb");
>-	unregister_die_notifier(&kgdb_notifier);
>-}
>-
>-/**
>- *	kgdb_skipexception - Bail out of KGDB when we've been triggered.
>- *	@exception: Exception vector number
>- *	@regs: Current &struct pt_regs.
>- *
>- *	On some architectures we need to skip a breakpoint exception when
>- *	it occurs after a breakpoint has been removed.
>- *
>- * Skip an int3 exception when it occurs after a breakpoint has been
>- * removed. Backtrack eip by 1 since the int3 would have caused it to
>- * increment by 1.
>- */
>-int kgdb_skipexception(int exception, struct pt_regs *regs)
>-{
>-	if (exception == 3 && kgdb_isremovedbreak(regs->ip - 1)) {
>-		regs->ip -= 1;
>-		return 1;
>-	}
>-	return 0;
>-}
>-
>-unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs)
>-{
>-	if (exception == 3)
>-		return instruction_pointer(regs) - 1;
>-	return instruction_pointer(regs);
>-}
>-
>-void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip)
>-{
>-	regs->ip = ip;
>-}
>-
>-int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
>-{
>-	int err;
>-
>-	bpt->type = BP_BREAKPOINT;
>-	err = copy_from_kernel_nofault(bpt->saved_instr, (char *)bpt->bpt_addr,
>-				BREAK_INSTR_SIZE);
>-	if (err)
>-		return err;
>-	err = copy_to_kernel_nofault((char *)bpt->bpt_addr,
>-				 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);
>-	if (!err)
>-		return err;
>-	/*
>-	 * It is safe to call text_poke_kgdb() because normal kernel execution
>-	 * is stopped on all cores, so long as the text_mutex is not locked.
>-	 */
>-	if (mutex_is_locked(&text_mutex))
>-		return -EBUSY;
>-	text_poke_kgdb((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,
>-		       BREAK_INSTR_SIZE);
>-	bpt->type = BP_POKE_BREAKPOINT;
>-
>-	return 0;
>-}
>-
>-int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
>-{
>-	if (bpt->type != BP_POKE_BREAKPOINT)
>-		goto knl_write;
>-	/*
>-	 * It is safe to call text_poke_kgdb() because normal kernel execution
>-	 * is stopped on all cores, so long as the text_mutex is not locked.
>-	 */
>-	if (mutex_is_locked(&text_mutex))
>-		goto knl_write;
>-	text_poke_kgdb((void *)bpt->bpt_addr, bpt->saved_instr,
>-		       BREAK_INSTR_SIZE);
>-	return 0;
>-
>-knl_write:
>-	return copy_to_kernel_nofault((char *)bpt->bpt_addr,
>-				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);
>-}
>-
>-const struct kgdb_arch arch_kgdb_ops = {
>-	/* Breakpoint instruction: */
>-	.gdb_bpt_instr		= { 0xcc },
>-	.flags			= KGDB_HW_BREAKPOINT,
>-	.set_hw_breakpoint	= kgdb_set_hw_break,
>-	.remove_hw_breakpoint	= kgdb_remove_hw_break,
>-	.disable_hw_break	= kgdb_disable_hw_debug,
>-	.remove_all_hw_break	= kgdb_remove_all_hw_break,
>-	.correct_hw_break	= kgdb_correct_hw_break,
>-};
>diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
>index 133ff20caccd..65707e4cffae 100644
>--- a/arch/x86/kernel/kprobes/core.c
>+++ b/arch/x86/kernel/kprobes/core.c
>@@ -37,7 +37,6 @@
> #include <linux/extable.h>
> #include <linux/kdebug.h>
> #include <linux/kallsyms.h>
>-#include <linux/kgdb.h>
> #include <linux/ftrace.h>
> #include <linux/kasan.h>
> #include <linux/objtool.h>
>@@ -311,15 +310,6 @@ static bool can_probe(unsigned long paddr)
> 		if (insn_decode_kernel(&insn, (void *)__addr) < 0)
> 			return false;
> 
>-#ifdef CONFIG_KGDB
>-		/*
>-		 * If there is a dynamically installed kgdb sw breakpoint,
>-		 * this function should not be probed.
>-		 */
>-		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
>-		    kgdb_has_hit_break(addr))
>-			return false;
>-#endif
> 		addr += insn.length;
> 	}
> 
>diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
>index 3f8fea52619f..821a416faf67 100644
>--- a/arch/x86/kernel/kprobes/opt.c
>+++ b/arch/x86/kernel/kprobes/opt.c
>@@ -15,7 +15,6 @@
> #include <linux/extable.h>
> #include <linux/kdebug.h>
> #include <linux
Is that really true? What if the debugging depends on specific hardware?

Re: [PATCH] x86: Drop KGDB support

[Peter Zijlstra]

On Wed, Oct 28, 2026 at 07:15:46AM -0700, H. Peter Anvin wrote:
> On October 28, 2026 5:21:24 AM PDT, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> >KGDB does some horrible things, and with everybody having access to
> >virtualization these days, there is really no reason to use it over
> >Qemu's gdb-server.
> >
> >Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

<snips a gazillion lines>

> Is that really true? What if the debugging depends on specific hardware?

Use device pass-through, emulate it, or printk() debug it.

Using KGDB can cause a ton of problems, it more or less stays stuck in
NMI context, which can terminally screw up the timekeeping code, it can
also cause the watchdogs to fire and there's endless annoyance with code
patching and breakpoints.

People have been trying to 'fix' the breakpoint code to be less broken
in the face of KGBD, but its all terrible and really not worth it. By
fat the sanest option is to just delete KGDB as proposed here.

Also, when was the last time you used KGDB? I think I've tried it once,
some 20 years ago, and haven't bothered since -- it was *that* good :-)

Re: [PATCH] x86: Drop KGDB support

[Dave Hansen]

On 10/28/26 07:26, Peter Zijlstra wrote:
...
> Also, when was the last time you used KGDB? I think I've tried it once,
> some 20 years ago, and haven't bothered since -- it was *that* good 🙂

I can't remember the last time I used it. I also grepped through all of
my stashed-away kernel configs I've been using for the past 15 or so
years. The only place I even see it configured in is in distro-derived
configs. None of my trimmed down debug configs.

There seems to be approximately one clear commit that shows anyone using
the x86 kgdb.c in the last decade:

	commit 71ab8323cc357c68985a2d6fc6cfc22b1dbbc1c3
	Author: Matt Mullins <mmullins@fb.com>
	Date:   Fri May 31 12:47:54 2019 -0700

	    x86/kgdb: Return 0 from kgdb_arch_set_breakpoint()

The only question for me at this point would be whether we should just
config it out for a couple of releases rather than removing it outright.