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

[firefly-linux-kernel-4.4.55.git] / arch / x86 / kernel / tsc.c

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 84d27356c3d017f49a8690d2a6b0e83cb1cd7b87..3e1c057e98fe039325eed2056d8960fa52f023c4 100644 (file)
--- 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;