From 41d49d4e6abf4fbfe76ad09a4dbedaf749ad11a1 Mon Sep 17 00:00:00 2001 From: "Borislav Petkov (AMD)" Date: Mon, 14 Apr 2025 15:33:19 +0200 Subject: [PATCH] x86/process: Move the buffer clearing before MONITOR Commit 8e786a85c0a3c0fffae6244733fb576eeabd9dec upstream. Move the VERW clearing before the MONITOR so that VERW doesn't disarm it and the machine never enters C1. Original idea by Kim Phillips . Suggested-by: Andrew Cooper Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/mwait.h | 16 +++++++++++----- arch/x86/kernel/process.c | 15 ++++++++++++--- 2 files changed, 23 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index 2c6020729dd14..d938792c11d97 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -44,8 +44,6 @@ static inline void __monitorx(const void *eax, unsigned long ecx, static inline void __mwait(unsigned long eax, unsigned long ecx) { - x86_idle_clear_cpu_buffers(); - /* "mwait %eax, %ecx;" */ asm volatile(".byte 0x0f, 0x01, 0xc9;" :: "a" (eax), "c" (ecx)); @@ -89,7 +87,6 @@ static inline void __mwaitx(unsigned long eax, unsigned long ebx, static inline void __sti_mwait(unsigned long eax, unsigned long ecx) { - x86_idle_clear_cpu_buffers(); /* "mwait %eax, %ecx;" */ asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" @@ -108,6 +105,11 @@ static inline void __sti_mwait(unsigned long eax, unsigned long ecx) */ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx) { + if (need_resched()) + return; + + x86_idle_clear_cpu_buffers(); + if (static_cpu_has_bug(X86_BUG_MONITOR) || !current_set_polling_and_test()) { if (static_cpu_has_bug(X86_BUG_CLFLUSH_MONITOR)) { mb(); @@ -116,9 +118,13 @@ static inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx) } __monitor((void *)¤t_thread_info()->flags, 0, 0); - if (!need_resched()) - __mwait(eax, ecx); + if (need_resched()) + goto out; + + __mwait(eax, ecx); } + +out: current_clr_polling(); } diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 50fe793498994..1138b999cb14b 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -887,6 +887,11 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c) */ static __cpuidle void mwait_idle(void) { + if (need_resched()) + return; + + x86_idle_clear_cpu_buffers(); + if (!current_set_polling_and_test()) { if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) { mb(); /* quirk */ @@ -895,13 +900,17 @@ static __cpuidle void mwait_idle(void) } __monitor((void *)¤t_thread_info()->flags, 0, 0); - if (!need_resched()) - __sti_mwait(0, 0); - else + if (need_resched()) { raw_local_irq_enable(); + goto out; + } + + __sti_mwait(0, 0); } else { raw_local_irq_enable(); } + +out: __current_clr_polling(); } -- 2.47.3