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Commit ce5f6824 authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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



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: default avatarH. Peter Anvin <hpa@linux.intel.com>
Acked-by: default avatarVenkatesh 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>
parent a68e5c94

arch/x86/kernel/smpboot.c

+19 −1
Original line number Diff line number Diff line
@@ -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);

	}