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x86: move rdtsc_barrier() into the TSC vread method 

The *fence instructions were moved to vsyscall_64.c by commit
cb9e35dce9.  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>
This commit is contained in:
Petr Tesarik 2009-05-25 11:02:02 +02:00 committed by Thomas Gleixner
parent cd86a536c8
commit 7d96fd41ca
2 changed files with 10 additions and 9 deletions
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11
arch/x86/kernel/tsc.c
View File

@ -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;

8
arch/x86/kernel/vsyscall_64.c
View File

@ -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;