diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2023-11-15 10:13:22 -0500 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-11-29 15:44:01 +0100 |
| commit | 7d09a052a3bdb62de9a86d43359d6c22eeaf105a (patch) | |
| tree | c1c7e22af6c6d635148e7f4618ebc0348ab52501 | |
| parent | 2cc14f52aeb78ce3f29677c2de1f06c0e91471ab (diff) | |
x86: Add a comment about the "magic" behind shadow sti before mwait
Add a note to make sure we never miss and break the requirements behind
it.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lkml.kernel.org/r/20231115151325.6262-2-frederic@kernel.org
| -rw-r--r-- | arch/x86/include/asm/mwait.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index 778df05f8539..341ee4f1d91e 100644 --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -87,6 +87,15 @@ static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx, :: "a" (eax), "b" (ebx), "c" (ecx)); } +/* + * Re-enable interrupts right upon calling mwait in such a way that + * no interrupt can fire _before_ the execution of mwait, ie: no + * instruction must be placed between "sti" and "mwait". + * + * This is necessary because if an interrupt queues a timer before + * executing mwait, it would otherwise go unnoticed and the next tick + * would not be reprogrammed accordingly before mwait ever wakes up. + */ static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx) { mds_idle_clear_cpu_buffers(); |