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x86, hotplug: In the MWAIT case of play_dead, CLFLUSH the cache line

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When we're using MWAIT for play_dead, explicitly CLFLUSH the cache
line before executing MONITOR.  This is a potential workaround for the
Xeon 7400 erratum AAI65 after having a spurious wakeup and returning
around the loop.  "Potential" here because it is not certain that that
erratum could actually trigger; however, the CLFLUSH should be
harmless.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Venkatesh Pallipadi <venki@google.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.kernel.org>
Cc: Len Brown <lenb@kernel.org>
This commit is contained in:
H. Peter Anvin 2010-09-20 13:04:45 -07:00
parent a68e5c94f7
commit ce5f68246b
1 changed files with 19 additions and 1 deletions
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20
arch/x86/kernel/smpboot.c
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@ -1394,9 +1394,12 @@ static inline void mwait_play_dead(void)
unsigned int highest_cstate = 0;
unsigned int highest_subcstate = 0;
int i;
void *mwait_ptr;
if (!cpu_has(&current_cpu_data, X86_FEATURE_MWAIT))
return;
if (!cpu_has(&current_cpu_data, X86_FEATURE_CLFLSH))
return;
if (current_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
return;
@ -1422,10 +1425,25 @@ static inline void mwait_play_dead(void)
(highest_subcstate - 1);
}
/*
* This should be a memory location in a cache line which is
* unlikely to be touched by other processors. The actual
* content is immaterial as it is not actually modified in any way.
*/
mwait_ptr = &current_thread_info()->flags;
wbinvd();
while (1) {
__monitor(&current_thread_info()->flags, 0, 0);
/*
* The CLFLUSH is a workaround for erratum AAI65 for
* the Xeon 7400 series. It's not clear it is actually
* needed, but it should be harmless in either case.
* The WBINVD is insufficient due to the spurious-wakeup
* case where we return around the loop.
*/
clflush(mwait_ptr);
__monitor(mwait_ptr, 0, 0);
mb();
__mwait(eax, 0);
}