x86: move rdtsc_barrier() into the TSC vread method

The *fence instructions were moved to vsyscall_64.c by commit
cb9e35dce94a1b9c59d46224e8a94377d673e204.  But this breaks the
vDSO, because vread methods are also called from there.

Besides, the synchronization might be unnecessary for other
time sources than TSC.

[ Impact: fix potential time warp in VDSO ]

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
LKML-Reference: <9d0ea9ea0f866bdc1f4d76831221ae117f11ea67.1243241859.git.ptesarik@suse.cz>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>

1 files changed, 0 insertions, 8 deletions

diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index 44153afc9067..25ee06a80aad 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -132,15 +132,7 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
                         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;