HVM-570 KVM: Fix wallclock version writing race

1 files changed, 7 insertions, 1 deletions

diff --git a/kvm_x86.c b/kvm_x86.c
index b83dbf0..010dfc2 100644
--- a/kvm_x86.c
+++ b/kvm_x86.c
@@ -652,13 +652,19 @@ do_set_msr(struct kvm_vcpu *vcpu, unsigned index, uint64_t *data)
 static void
 kvm_write_wall_clock(struct kvm *kvm, gpa_t wall_clock)
 {
-	static int version;
+	int version;
 	struct pvclock_wall_clock wc;
 	struct timespec boot;
 
 	if (!wall_clock)
 		return;
 
+	if (kvm_read_guest(kvm, wall_clock, &version, sizeof (version)) != 0)
+		return;
+
+	if (version & 1)
+		version++;	/* first time write, random junk */
+
 	version++;
 
 	kvm_write_guest(kvm, wall_clock, &version, sizeof (version));