Commit 78fd8c72 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

x86/vdso/pvclock: Protect STABLE check with the seqcount

If the clock becomes unstable while we're reading it, we need to
bail.  We can do this by simply moving the check into the
seqcount loop.
Reported-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Alexander Graf <agraf@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/755dcedb17269e1d7ce12a9a713dea303835137e.1451949191.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 4eaffdd5
...@@ -126,23 +126,23 @@ static notrace cycle_t vread_pvclock(int *mode) ...@@ -126,23 +126,23 @@ static notrace cycle_t vread_pvclock(int *mode)
* *
* On Xen, we don't appear to have that guarantee, but Xen still * On Xen, we don't appear to have that guarantee, but Xen still
* supplies a valid seqlock using the version field. * supplies a valid seqlock using the version field.
*
* We only do pvclock vdso timing at all if * We only do pvclock vdso timing at all if
* PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to * PVCLOCK_TSC_STABLE_BIT is set, and we interpret that bit to
* mean that all vCPUs have matching pvti and that the TSC is * mean that all vCPUs have matching pvti and that the TSC is
* synced, so we can just look at vCPU 0's pvti. * synced, so we can just look at vCPU 0's pvti.
*/ */
if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
*mode = VCLOCK_NONE;
return 0;
}
do { do {
version = pvti->version; version = pvti->version;
smp_rmb(); smp_rmb();
if (unlikely(!(pvti->flags & PVCLOCK_TSC_STABLE_BIT))) {
*mode = VCLOCK_NONE;
return 0;
}
tsc = rdtsc_ordered(); tsc = rdtsc_ordered();
pvti_tsc_to_system_mul = pvti->tsc_to_system_mul; pvti_tsc_to_system_mul = pvti->tsc_to_system_mul;
pvti_tsc_shift = pvti->tsc_shift; pvti_tsc_shift = pvti->tsc_shift;
......
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