From: Peter Zijlstra peterz@infradead.org
[ Upstream commit a1a5482a2c6e38a3ebed32e571625c56a8cc41a6 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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 13d838e6030b..a9c7efd4b794 100644 --- a/arch/x86/mm/extable.c +++ b/arch/x86/mm/extable.c @@ -86,16 +86,18 @@ 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 861e606b820f..b7bce4983638 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); \ })