[Xen-changelog] [xen stable-4.2] x86/Intel: work around Xeon 7400 series erratum AAI65

[patchbot@xxxxxxx]

commit 3327c530101c877f303931ba44487bc48b9f0646
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Apr 9 11:38:20 2014 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Apr 9 11:38:20 2014 +0200

    x86/Intel: work around Xeon 7400 series erratum AAI65
    
    Linux commit 40e2d7f9b5dae048789c64672bf3027fbb663ffa ("x86 idle:
    Repair large-server 50-watt idle-power regression") tells us that this
    applies not just to the named Xeon 7400 series, but also NHM-EX and
    WSM-EX; sadly Intel's documentation is so badly searchable that I
    wasn't able to locate the respective errata (and hence can't quote
    their numbers here).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 96d1b237ae9b2f2718bb1c59820701f17d3d86e0
    master date: 2014-03-17 16:47:22 +0100
---
 xen/arch/x86/acpi/cpu_idle.c     |    3 +++
 xen/arch/x86/cpu/intel.c         |    7 +++++++
 xen/include/asm-x86/cpufeature.h |    1 +
 3 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/acpi/cpu_idle.c b/xen/arch/x86/acpi/cpu_idle.c
index 989d034..f956929 100644
--- a/xen/arch/x86/acpi/cpu_idle.c
+++ b/xen/arch/x86/acpi/cpu_idle.c
@@ -276,6 +276,9 @@ static void mwait_idle_with_hints(unsigned long eax, 
unsigned long ecx)
     unsigned int cpu = smp_processor_id();
     s_time_t expires = per_cpu(timer_deadline, cpu);
 
+    if ( boot_cpu_has(X86_FEATURE_CLFLUSH_MONITOR) )
+        clflush((void *)&mwait_wakeup(cpu));
+
     __monitor((void *)&mwait_wakeup(cpu), 0, 0);
     smp_mb();
 
diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index 0d5f25f..348d36f 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -154,6 +154,9 @@ void __devinit early_intel_workaround(struct cpuinfo_x86 *c)
 /*
  * P4 Xeon errata 037 workaround.
  * Hardware prefetcher may cause stale data to be loaded into the cache.
+ *
+ * Xeon 7400 erratum AAI65 (and further newer Xeons)
+ * MONITOR/MWAIT may have excessive false wakeups
  */
 static void __devinit Intel_errata_workarounds(struct cpuinfo_x86 *c)
 {
@@ -168,6 +171,10 @@ static void __devinit Intel_errata_workarounds(struct 
cpuinfo_x86 *c)
                        wrmsr (MSR_IA32_MISC_ENABLE, lo, hi);
                }
        }
+
+       if (c->x86 == 6 && cpu_has_clflush &&
+           (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47))
+               set_bit(X86_FEATURE_CLFLUSH_MONITOR, c->x86_capability);
 }
 
 
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index 4f43b2e..3837b11 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -80,6 +80,7 @@
 #define X86_FEATURE_TSC_RELIABLE (3*32+12) /* TSC is known to be reliable */
 #define X86_FEATURE_XTOPOLOGY    (3*32+13) /* cpu topology enum extensions */
 #define X86_FEATURE_CPUID_FAULTING (3*32+14) /* cpuid faulting */
+#define X86_FEATURE_CLFLUSH_MONITOR (3*32+15) /* clflush reqd with monitor */
 
 /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */
 #define X86_FEATURE_XMM3       (4*32+ 0) /* Streaming SIMD Extensions-3 */
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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