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x86/process: Move the buffer clearing before MONITOR

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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 <kim.phillips@amd.com>.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Borislav Petkov (AMD)
2025-04-14 15:33:19 +02:00
committed by Greg Kroah-Hartman
parent 6fb766d53f
commit 8c19449058
2 changed files with 27 additions and 14 deletions
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15
arch/x86/include/asm/mwait.h
View File

@@ -44,8 +44,6 @@ static __always_inline void __monitorx(const void *eax, unsigned long ecx,
static __always_inline void __mwait(unsigned long eax, unsigned long ecx) static __always_inline void __mwait(unsigned long eax, unsigned long ecx)
{ {
x86_idle_clear_cpu_buffers();
/* "mwait %eax, %ecx;" */ /* "mwait %eax, %ecx;" */
asm volatile(".byte 0x0f, 0x01, 0xc9;" asm volatile(".byte 0x0f, 0x01, 0xc9;"
:: "a" (eax), "c" (ecx)); :: "a" (eax), "c" (ecx));
@@ -89,7 +87,6 @@ static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx,
static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx) static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx)
{ {
x86_idle_clear_cpu_buffers();
/* "mwait %eax, %ecx;" */ /* "mwait %eax, %ecx;" */
asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
@@ -108,13 +105,20 @@ static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx)
*/ */
static __always_inline void mwait_idle_with_hints(unsigned long eax, unsigned long ecx) static __always_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_MONITOR) || !current_set_polling_and_test()) {
const void *addr = &current_thread_info()->flags; const void *addr = &current_thread_info()->flags;
alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr)); alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr));
__monitor(addr, 0, 0); __monitor(addr, 0, 0);
if (!need_resched()) { if (need_resched())
goto out;
if (ecx & 1) { if (ecx & 1) {
__mwait(eax, ecx); __mwait(eax, ecx);
} else { } else {
@@ -122,7 +126,8 @@ static __always_inline void mwait_idle_with_hints(unsigned long eax, unsigned lo
raw_local_irq_disable(); raw_local_irq_disable();
} }
} }
}
out:
current_clr_polling(); current_clr_polling();
} }

12
arch/x86/kernel/process.c
View File

@@ -928,16 +928,24 @@ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
*/ */
static __cpuidle void mwait_idle(void) static __cpuidle void mwait_idle(void)
{ {
if (need_resched())
return;
x86_idle_clear_cpu_buffers();
if (!current_set_polling_and_test()) { if (!current_set_polling_and_test()) {
const void *addr = &current_thread_info()->flags; const void *addr = &current_thread_info()->flags;
alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr)); alternative_input("", "clflush (%[addr])", X86_BUG_CLFLUSH_MONITOR, [addr] "a" (addr));
__monitor(addr, 0, 0); __monitor(addr, 0, 0);
if (!need_resched()) { if (need_resched())
goto out;
__sti_mwait(0, 0); __sti_mwait(0, 0);
raw_local_irq_disable(); raw_local_irq_disable();
} }
}
out:
__current_clr_polling(); __current_clr_polling();
} }