x86: Implement support to synchronize RDTSC with LFENCE on Intel CPUs

According to Intel RDTSC can be always synchronized with LFENCE
on all current CPUs. Implement the necessary CPUID bit for that.

It is unclear yet if that is true for all future CPUs too,
but if there's another way the kernel can be always updated.

Cc: asit.k.mallick@intel.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>

1 files changed, 1 insertions, 4 deletions

diff --git a/arch/x86/kernel/setup_64.c b/arch/x86/kernel/setup_64.c
index 2139aa6ac469..bc7758ea06af 100644
--- a/arch/x86/kernel/setup_64.c
+++ b/arch/x86/kernel/setup_64.c
@@ -888,10 +888,7 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)
                 set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
         if (c->x86 == 6)
                 set_cpu_cap(c, X86_FEATURE_REP_GOOD);
-        if (c->x86 == 15)
-                set_cpu_cap(c, X86_FEATURE_SYNC_RDTSC);
-        else
-                clear_cpu_cap(c, X86_FEATURE_SYNC_RDTSC);
+        set_cpu_cap(c, X86_FEATURE_LFENCE_RDTSC);
         c->x86_max_cores = intel_num_cpu_cores(c);
 
         srat_detect_node();