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@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Stephane Eranian <eranian@google.com>
Link: https://lkml.kernel.org/r/YqyVFsbviKjVGGZ9@worktop.programming.kicks-ass.net

diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index dba2197..331310c 100644 (file)
--- 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 (file)
--- 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);                                \
        })