Merge branch 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-vdso-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86: move rdtsc_barrier() into the TSC vread method

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 84d27356c3d..3e1c057e98f 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -710,7 +710,16 @@ static cycle_t read_tsc(struct clocksource *cs)
 #ifdef CONFIG_X86_64
 static cycle_t __vsyscall_fn vread_tsc(void)
 {
-        cycle_t ret = (cycle_t)vget_cycles();
+        cycle_t ret;
+
+        /*
+         * 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();
+        ret = (cycle_t)vget_cycles();
+        rdtsc_barrier();
 
         return ret >= __vsyscall_gtod_data.clock.cycle_last ?
                 ret : __vsyscall_gtod_data.clock.cycle_last;