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Subject[patch 046/108] x86: move rdtsc_barrier() into the TSC vread method
2.6.30-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Petr Tesarik <ptesarik@suse.cz>

commit 7d96fd41cadc55f4e00231c8c71b8e25c779f122 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/x86/kernel/tsc.c | 11 ++++++++++-
arch/x86/kernel/vsyscall_64.c | 8 --------
2 files changed, 10 insertions(+), 9 deletions(-)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -710,7 +710,16 @@ static cycle_t read_tsc(struct clocksour
#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;
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -132,15 +132,7 @@ static __always_inline void do_vgettimeo
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;



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