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pvclock: Add CPU barriers to get correct version value 

Protocol for the "version" fields is: hypervisor raises it (making it
uneven) before it starts updating the fields and raises it again (making
it even) when it is done.  Thus the guest can make sure the time values
it got are consistent by checking the version before and after reading
them.

Add CPU barries after getting version value just like what function
vread_pvclock does, because all of callees in this function is inline.

Fixes: 502dfeff23
Cc: stable@vger.kernel.org
Signed-off-by: Minfei Huang <mnghuan@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Minfei Huang 2016-05-27 14:17:10 +08:00 committed by Paolo Bonzini
parent 4c2e07c6a2
commit 749d088b8e
2 changed files with 6 additions and 0 deletions
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2
arch/x86/include/asm/pvclock.h
View File

@ -85,6 +85,8 @@ unsigned __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src,
u8 ret_flags; u8 ret_flags;
version = src->version; version = src->version;
/* Make the latest version visible */
smp_rmb();
offset = pvclock_get_nsec_offset(src); offset = pvclock_get_nsec_offset(src);
ret = src->system_time + offset; ret = src->system_time + offset;

4
arch/x86/kernel/pvclock.c
View File

@ -66,6 +66,8 @@ u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
do { do {
version = __pvclock_read_cycles(src, &ret, &flags); version = __pvclock_read_cycles(src, &ret, &flags);
/* Make sure that the version double-check is last. */
smp_rmb();
} while ((src->version & 1) || version != src->version); } while ((src->version & 1) || version != src->version);
return flags & valid_flags; return flags & valid_flags;
@ -80,6 +82,8 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
do { do {
version = __pvclock_read_cycles(src, &ret, &flags); version = __pvclock_read_cycles(src, &ret, &flags);
/* Make sure that the version double-check is last. */
smp_rmb();
} while ((src->version & 1) || version != src->version); } while ((src->version & 1) || version != src->version);
if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) { if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {