x86: implement support to synchronize RDTSC through MFENCE on AMD CPUs
According to AMD RDTSC can be synchronized through MFENCE.
Implement the necessary CPUID bit for that.
Cc: andreas.herrmann3@amd.com
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 1ff88c7..aaa8101 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -301,6 +301,9 @@
/* K6s reports MCEs but don't actually have all the MSRs */
if (c->x86 < 6)
clear_bit(X86_FEATURE_MCE, c->x86_capability);
+
+ if (cpu_has_xmm)
+ set_bit(X86_FEATURE_MFENCE_RDTSC, c->x86_capability);
}
static unsigned int __cpuinit amd_size_cache(struct cpuinfo_x86 * c, unsigned int size)
diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 0240910..2139aa6 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -746,8 +746,8 @@
if (c->x86 == 0xf || c->x86 == 0x10 || c->x86 == 0x11)
set_cpu_cap(c, X86_FEATURE_K8);
- /* RDTSC can be speculated around */
- clear_cpu_cap(c, X86_FEATURE_SYNC_RDTSC);
+ /* MFENCE stops RDTSC speculation */
+ set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC);
/* Family 10 doesn't support C states in MWAIT so don't use it */
if (c->x86 == 0x10 && !force_mwait)