x86, hotplug: In the MWAIT case of play_dead, CLFLUSH the cache line (ce5f6824) · Commits · 戴 / test

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>

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);
		}

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