linux-kernel - [tip: x86/core] x86/extable: Fix ex_handler

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Message-ID: <165839352078.15455.154258296152260339.tip-bot2@tip-bot2>
Date:   Thu, 21 Jul 2022 08:52:00 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Stephane Eranian <eranian@...gle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/core] x86/extable: Fix ex_handler_msr() print condition

The following commit has been merged into the x86/core branch of tip:

Commit-ID:     a1a5482a2c6e38a3ebed32e571625c56a8cc41a6
Gitweb:        https://git.kernel.org/tip/a1a5482a2c6e38a3ebed32e571625c56a8cc41a6
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Fri, 17 Jun 2022 16:52:06 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 21 Jul 2022 10:39:42 +02:00

x86/extable: Fix ex_handler_msr() print condition

On Fri, Jun 17, 2022 at 02:08:52PM +0300, Stephane Eranian wrote:
> Some changes to the way invalid MSR accesses are reported by the
> kernel is causing some problems with messages printed on the
> console.
>
> We have seen several cases of ex_handler_msr() printing invalid MSR
> accesses once but the callstack multiple times causing confusion on
> the console.

> The problem here is that another earlier commit (5.13):
>
> a358f40600b3 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality")
>
> Modifies all the pr_*_once() calls to always return true claiming
> that no caller is ever checking the return value of the functions.
>
> This is why we are seeing the callstack printed without the
> associated printk() msg.

Extract the ONCE_IF(cond) part into __ONCE_LTE_IF() and use that to
implement DO_ONCE_LITE_IF() and fix the extable code.

Fixes: a358f40600b3 ("once: implement DO_ONCE_LITE for non-fast-path "do once" functionality")
Reported-by: Stephane Eranian <eranian@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Stephane Eranian <eranian@...gle.com>
Link: https://lkml.kernel.org/r/YqyVFsbviKjVGGZ9@worktop.programming.kicks-ass.net
---
 arch/x86/mm/extable.c     | 16 +++++++++-------
 include/linux/once_lite.h | 20 ++++++++++++++++----
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index dba2197..331310c 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -94,16 +94,18 @@ static bool ex_handler_copy(const struct exception_table_entry *fixup,
 static bool ex_handler_msr(const struct exception_table_entry *fixup,
 			   struct pt_regs *regs, bool wrmsr, bool safe, int reg)
 {
-	if (!safe && wrmsr &&
-	    pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",
-			 (unsigned int)regs->cx, (unsigned int)regs->dx,
-			 (unsigned int)regs->ax,  regs->ip, (void *)regs->ip))
+	if (__ONCE_LITE_IF(!safe && wrmsr)) {
+		pr_warn("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pS)\n",
+			(unsigned int)regs->cx, (unsigned int)regs->dx,
+			(unsigned int)regs->ax,  regs->ip, (void *)regs->ip);
 		show_stack_regs(regs);
+	}
 
-	if (!safe && !wrmsr &&
-	    pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",
-			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
+	if (__ONCE_LITE_IF(!safe && !wrmsr)) {
+		pr_warn("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pS)\n",
+			(unsigned int)regs->cx, regs->ip, (void *)regs->ip);
 		show_stack_regs(regs);
+	}
 
 	if (!wrmsr) {
 		/* Pretend that the read succeeded and returned 0. */
diff --git a/include/linux/once_lite.h b/include/linux/once_lite.h
index 861e606..b7bce49 100644
--- a/include/linux/once_lite.h
+++ b/include/linux/once_lite.h
@@ -9,15 +9,27 @@
  */
 #define DO_ONCE_LITE(func, ...)						\
 	DO_ONCE_LITE_IF(true, func, ##__VA_ARGS__)
-#define DO_ONCE_LITE_IF(condition, func, ...)				\
+
+#define __ONCE_LITE_IF(condition)					\
 	({								\
 		static bool __section(".data.once") __already_done;	\
-		bool __ret_do_once = !!(condition);			\
+		bool __ret_cond = !!(condition);			\
+		bool __ret_once = false;				\
 									\
-		if (unlikely(__ret_do_once && !__already_done)) {	\
+		if (unlikely(__ret_cond && !__already_done)) {		\
 			__already_done = true;				\
-			func(__VA_ARGS__);				\
+			__ret_once = true;				\
 		}							\
+		unlikely(__ret_once);					\
+	})
+
+#define DO_ONCE_LITE_IF(condition, func, ...)				\
+	({								\
+		bool __ret_do_once = !!(condition);			\
+									\
+		if (__ONCE_LITE_IF(__ret_do_once))			\
+			func(__VA_ARGS__);				\
+									\
 		unlikely(__ret_do_once);				\
 	})