Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 2/7] x86: Add a comment about the "magic" behind shadow sti before mwait | Date | Fri, 24 Nov 2023 23:32:21 +0100 |
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Add a note to make sure we never miss and break the requirements behind it.
Acked-by: Rafael J. Wysocki <rafael@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> --- arch/x86/include/asm/mwait.h | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h index bae83810505b..920426d691ce 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(); -- 2.42.1
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