x86: clean up rdtsc_barrier() use

Impact: cleanup

Move rdtsc_barrier() use to vsyscall_64.c where it's relied on,
and point out its role in the context of its use.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 10 insertions, 5 deletions

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 9cd83a8e40d5..700aeb8d2098 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -44,11 +44,7 @@ static __always_inline cycles_t vget_cycles(void)
         if (!cpu_has_tsc)
                 return 0;
 #endif
-        rdtsc_barrier();
-        cycles = (cycles_t)__native_read_tsc();
-        rdtsc_barrier();
-
-        return cycles;
+        return (cycles_t)__native_read_tsc();
 }
 
 extern void tsc_init(void);
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 0b8b6690a86d..ebf2f12900f5 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -128,7 +128,16 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
                         gettimeofday(tv,NULL);
                         return;
                 }
+
+                /*
+                 * Surround the RDTSC by barriers, to make sure it's not
+                 * speculated to outside the seqlock critical section and
+                 * does not cause time warps:
+                 */
+                rdtsc_barrier();
                 now = vread();
+                rdtsc_barrier();
+
                 base = __vsyscall_gtod_data.clock.cycle_last;
                 mask = __vsyscall_gtod_data.clock.mask;
                 mult = __vsyscall_gtod_data.clock.mult;