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KVM: Fix wallclock version writing race

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Wallclock writing uses an unprotected global variable to hold the version;
this can cause one guest to interfere with another if both write their
wallclock at the same time.

Acked-by: Glauber Costa <glommer@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
(cherry picked from commit 9ed3c444ab)
This commit is contained in:
Avi Kivity 2010-05-04 15:00:37 +03:00 committed by Greg Kroah-Hartman
parent 4a277f9cb8
commit 0890bb8d95
1 changed files with 10 additions and 2 deletions
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12
arch/x86/kvm/x86.c
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@ -554,14 +554,22 @@ static int do_set_msr(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
static void kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
{
static int version;
int version;
int r;
struct pvclock_wall_clock wc;
struct timespec boot;
if (!wall_clock)
return;
version++;
r = kvm_read_guest(kvm, wall_clock, &version, sizeof(version));
if (r)
return;
if (version & 1)
++version; /* first time write, random junk */
++version;
kvm_write_guest(kvm, wall_clock, &version, sizeof(version));