Commit 7d09a052 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Peter Zijlstra
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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: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarRafael J. Wysocki <rafael@kernel.org>
Link: https://lkml.kernel.org/r/20231115151325.6262-2-frederic@kernel.org
parent 2cc14f52

arch/x86/include/asm/mwait.h

+9 −0
Original line number Diff line number Diff line
@@ -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();