From: H. Peter Anvin <[email protected]> ===================================================================== | This is a commit scheduled for the next v2.6.34 longterm release. | | If you see a problem with using this for longterm, please comment.| =====================================================================
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 <[email protected]> Acked-by: Venkatesh Pallipadi <[email protected]> Cc: Asit Mallick <[email protected]> Cc: Arjan van de Ven <[email protected]> Cc: Len Brown <[email protected]> Signed-off-by: Paul Gortmaker <[email protected]> --- arch/x86/kernel/smpboot.c | 20 +++++++++++++++++++- 1 files changed, 19 insertions(+), 1 deletions(-) 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 _______________________________________________ stable mailing list [email protected] http://linux.kernel.org/mailman/listinfo/stable
