x86: add clflush before monitor for Intel 7400 series

For Intel 7400 series CPUs, the recommendation is to use a clflush on the
monitored address just before monitor and mwait pair [1].

This clflush makes sure that there are no false wakeups from mwait when the
monitored address was recently written to.

[1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series"
    section in specification update document of 7400 series
    http://download.intel.com/design/xeon/specupdt/32033601.pdf

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 430e5c38a544..24ff26a38ade 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -291,6 +291,9 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
                 ds_init_intel(c);
         }
 
+        if (c->x86 == 6 && c->x86_model == 29 && cpu_has_clflush)
+                set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR);
+
 #ifdef CONFIG_X86_64
         if (c->x86 == 15)
                 c->x86_cache_alignment = c->x86_clflush_size * 2;