[tip: core/entry] riscv: entry: Convert ret_from_fork() to C

["tip-bot2 for Charlie Jenkins" <tip-bot2@linutronix.de>]

The following commit has been merged into the core/entry branch of tip:

Commit-ID:     f955aa8723a65759e920d4de8e5d076cef412afc
Gitweb:        https://git.kernel.org/tip/f955aa8723a65759e920d4de8e5d076cef412afc
Author:        Charlie Jenkins <charlie@rivosinc.com>
AuthorDate:    Thu, 20 Mar 2025 10:29:21 -07:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 29 Apr 2025 08:27:10 +02:00

riscv: entry: Convert ret_from_fork() to C

Move the main section of ret_from_fork() to C to allow inlining of
syscall_exit_to_user_mode().

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/all/20250320-riscv_optimize_entry-v6-1-63e187e26041@rivosinc.com

---
 arch/riscv/include/asm/asm-prototypes.h |  1 +
 arch/riscv/kernel/entry.S               | 15 ++++++---------
 arch/riscv/kernel/process.c             | 14 ++++++++++++--
 3 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/include/asm/asm-prototypes.h b/arch/riscv/include/asm/asm-prototypes.h
index cd627ec..733ff60 100644
--- a/arch/riscv/include/asm/asm-prototypes.h
+++ b/arch/riscv/include/asm/asm-prototypes.h
@@ -52,6 +52,7 @@ DECLARE_DO_ERROR_INFO(do_trap_ecall_s);
 DECLARE_DO_ERROR_INFO(do_trap_ecall_m);
 DECLARE_DO_ERROR_INFO(do_trap_break);
 
+asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_regs *regs);
 asmlinkage void handle_bad_stack(struct pt_regs *regs);
 asmlinkage void do_page_fault(struct pt_regs *regs);
 asmlinkage void do_irq(struct pt_regs *regs);
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 33a5a9f..b2dc5e7 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -319,17 +319,14 @@ SYM_CODE_END(handle_kernel_stack_overflow)
 ASM_NOKPROBE(handle_kernel_stack_overflow)
 #endif
 
-SYM_CODE_START(ret_from_fork)
+SYM_CODE_START(ret_from_fork_asm)
 	call schedule_tail
-	beqz s0, 1f	/* not from kernel thread */
-	/* Call fn(arg) */
-	move a0, s1
-	jalr s0
-1:
-	move a0, sp /* pt_regs */
-	call syscall_exit_to_user_mode
+	move a0, s1 /* fn_arg */
+	move a1, s0 /* fn */
+	move a2, sp /* pt_regs */
+	call ret_from_fork
 	j ret_from_exception
-SYM_CODE_END(ret_from_fork)
+SYM_CODE_END(ret_from_fork_asm)
 
 #ifdef CONFIG_IRQ_STACKS
 /*
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 7c244de..7b0a0bf 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -17,7 +17,9 @@
 #include <linux/ptrace.h>
 #include <linux/uaccess.h>
 #include <linux/personality.h>
+#include <linux/entry-common.h>
 
+#include <asm/asm-prototypes.h>
 #include <asm/unistd.h>
 #include <asm/processor.h>
 #include <asm/csr.h>
@@ -36,7 +38,7 @@ unsigned long __stack_chk_guard __read_mostly;
 EXPORT_SYMBOL(__stack_chk_guard);
 #endif
 
-extern asmlinkage void ret_from_fork(void);
+extern asmlinkage void ret_from_fork_asm(void);
 
 void noinstr arch_cpu_idle(void)
 {
@@ -206,6 +208,14 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 	return 0;
 }
 
+asmlinkage void ret_from_fork(void *fn_arg, int (*fn)(void *), struct pt_regs *regs)
+{
+	if (unlikely(fn))
+		fn(fn_arg);
+
+	syscall_exit_to_user_mode(regs);
+}
+
 int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 {
 	unsigned long clone_flags = args->flags;
@@ -242,7 +252,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	p->thread.riscv_v_flags = 0;
 	if (has_vector() || has_xtheadvector())
 		riscv_v_thread_alloc(p);
-	p->thread.ra = (unsigned long)ret_from_fork;
+	p->thread.ra = (unsigned long)ret_from_fork_asm;
 	p->thread.sp = (unsigned long)childregs; /* kernel sp */
 	return 0;
 }