[patch 31/38] x86/calldepth: Add ret/call counting for debug

[Thomas Gleixner <tglx@linutronix.de>]

Add a debuigfs mechanism to validate the accounting, e.g. vs. call/ret
balance and to gather statistics about the stuffing to call ratio.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/nospec-branch.h |   32 +++++++++++++++++++--
 arch/x86/kernel/callthunks.c         |   51 +++++++++++++++++++++++++++++++++++
 arch/x86/lib/retpoline.S             |    7 ++++
 3 files changed, 86 insertions(+), 4 deletions(-)

--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -77,6 +77,23 @@
  */
 
 #ifdef CONFIG_CALL_DEPTH_TRACKING
+
+#ifdef CONFIG_CALL_THUNKS_DEBUG
+# define CALL_THUNKS_DEBUG_INC_CALLS				\
+	incq	%gs:__x86_call_count;
+# define CALL_THUNKS_DEBUG_INC_RETS				\
+	incq	%gs:__x86_ret_count;
+# define CALL_THUNKS_DEBUG_INC_STUFFS				\
+	incq	%gs:__x86_stuffs_count;
+# define CALL_THUNKS_DEBUG_INC_CTXSW				\
+	incq	%gs:__x86_ctxsw_count;
+#else
+# define CALL_THUNKS_DEBUG_INC_CALLS
+# define CALL_THUNKS_DEBUG_INC_RETS
+# define CALL_THUNKS_DEBUG_INC_STUFFS
+# define CALL_THUNKS_DEBUG_INC_CTXSW
+#endif
+
 #define CREDIT_CALL_DEPTH					\
 	movq	$-1, PER_CPU_VAR(__x86_call_depth);
 
@@ -88,10 +105,12 @@
 #define RESET_CALL_DEPTH_FROM_CALL				\
 	mov	$0xfc, %rax;					\
 	shl	$56, %rax;					\
-	movq	%rax, PER_CPU_VAR(__x86_call_depth);
+	movq	%rax, PER_CPU_VAR(__x86_call_depth);		\
+	CALL_THUNKS_DEBUG_INC_CALLS
 
 #define INCREMENT_CALL_DEPTH					\
-	sarq	$5, %gs:__x86_call_depth
+	sarq	$5, %gs:__x86_call_depth;			\
+	CALL_THUNKS_DEBUG_INC_CALLS
 #else
 #define CREDIT_CALL_DEPTH
 #define RESET_CALL_DEPTH
@@ -127,7 +146,8 @@
 	dec	reg;				\
 	jnz	771b;				\
 						\
-	CREDIT_CALL_DEPTH
+	CREDIT_CALL_DEPTH			\
+	CALL_THUNKS_DEBUG_INC_CTXSW
 
 #ifdef __ASSEMBLY__
 
@@ -274,6 +294,12 @@ static inline void x86_set_skl_return_th
 }
 
 DECLARE_PER_CPU(u64, __x86_call_depth);
+#ifdef CONFIG_CALL_THUNKS_DEBUG
+DECLARE_PER_CPU(u64, __x86_call_count);
+DECLARE_PER_CPU(u64, __x86_ret_count);
+DECLARE_PER_CPU(u64, __x86_stuffs_count);
+DECLARE_PER_CPU(u64, __x86_ctxsw_count);
+#endif
 #else
 static inline void x86_set_skl_return_thunk(void) {}
 #endif
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -3,6 +3,7 @@
 #define pr_fmt(fmt) "callthunks: " fmt
 
 #include <linux/btree.h>
+#include <linux/debugfs.h>
 #include <linux/memory.h>
 #include <linux/moduleloader.h>
 #include <linux/set_memory.h>
@@ -32,6 +33,13 @@ static int __init debug_thunks(char *str
 	return 1;
 }
 __setup("debug-callthunks", debug_thunks);
+
+DEFINE_PER_CPU(u64, __x86_call_count);
+DEFINE_PER_CPU(u64, __x86_ret_count);
+DEFINE_PER_CPU(u64, __x86_stuffs_count);
+DEFINE_PER_CPU(u64, __x86_ctxsw_count);
+EXPORT_SYMBOL_GPL(__x86_ctxsw_count);
+
 #else
 #define prdbg(fmt, args...)	do { } while(0)
 #endif
@@ -530,3 +538,46 @@ void callthunks_module_free(struct modul
 	mutex_unlock(&text_mutex);
 }
 #endif /* CONFIG_MODULES */
+
+#if defined(CONFIG_CALL_THUNKS_DEBUG) && defined(CONFIG_DEBUG_FS)
+static int callthunks_debug_show(struct seq_file *m, void *p)
+{
+	unsigned long cpu = (unsigned long)m->private;
+
+	seq_printf(m, "C: %16llu R: %16llu S: %16llu X: %16llu\n,",
+		   per_cpu(__x86_call_count, cpu),
+		   per_cpu(__x86_ret_count, cpu),
+		   per_cpu(__x86_stuffs_count, cpu),
+		   per_cpu(__x86_ctxsw_count, cpu));
+	return 0;
+}
+
+static int callthunks_debug_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, callthunks_debug_show, inode->i_private);
+}
+
+static const struct file_operations dfs_ops = {
+	.open		= callthunks_debug_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int __init callthunks_debugfs_init(void)
+{
+	struct dentry *dir;
+	unsigned long cpu;
+
+	dir = debugfs_create_dir("callthunks", NULL);
+	for_each_possible_cpu(cpu) {
+		void *arg = (void *)cpu;
+		char name [10];
+
+		sprintf(name, "cpu%lu", cpu);
+		debugfs_create_file(name, 0644, dir, arg, &dfs_ops);
+	}
+	return 0;
+}
+__initcall(callthunks_debugfs_init);
+#endif
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -202,13 +202,18 @@ EXPORT_SYMBOL(__x86_return_thunk)
 	.align 64
 SYM_FUNC_START(__x86_return_skl)
 	ANNOTATE_NOENDBR
-	/* Keep the hotpath in a 16byte I-fetch */
+	/*
+	 * Keep the hotpath in a 16byte I-fetch for the non-debug
+	 * case.
+	 */
+	CALL_THUNKS_DEBUG_INC_RETS
 	shlq	$5, PER_CPU_VAR(__x86_call_depth)
 	jz	1f
 	ANNOTATE_UNRET_SAFE
 	ret
 	int3
 1:
+	CALL_THUNKS_DEBUG_INC_STUFFS
 	.rept	16
 	ANNOTATE_INTRA_FUNCTION_CALL
 	call	2f