| From b897edc98fb90cf722e5bf330ebc64bc04ae6eff Mon Sep 17 00:00:00 2001 |
| From: H. Peter Anvin <hpa@linux.intel.com> |
| Date: Mon, 20 Sep 2010 13:04:45 -0700 |
| Subject: [PATCH] x86, hotplug: In the MWAIT case of play_dead, CLFLUSH the |
| cache line |
| |
| commit ce5f68246bf2385d6174856708d0b746dc378f20 upstream. |
| |
| 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> |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c |
| index b283dbf..9a4fdc5 100644 |
| --- a/arch/x86/kernel/smpboot.c |
| +++ b/arch/x86/kernel/smpboot.c |
| @@ -1371,9 +1371,12 @@ 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(¤t_cpu_data, X86_FEATURE_MWAIT)) |
| return; |
| + if (!cpu_has(¤t_cpu_data, X86_FEATURE_CLFLSH)) |
| + return; |
| if (current_cpu_data.cpuid_level < CPUID_MWAIT_LEAF) |
| return; |
| |
| @@ -1399,10 +1402,25 @@ 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 = ¤t_thread_info()->flags; |
| + |
| wbinvd(); |
| |
| while (1) { |
| - __monitor(¤t_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); |
| } |
| -- |
| 1.7.4.4 |
| |