Avi noticed that we have to use guest's value for the version field, instead of keeping track of it ourselves. If we don't do that, the following situation can arise: vcpu->arch.hv_clock.version is initialized to zero. Guest reads version (result: 2) Guest starts reading data Live migration; vcpu->arch.hv_clock.version is zeroed Steal time update; vcpu->arch.hv_clock.version += 2; write to guest Guest continues reading data Guest reads version (result: 2) Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx> CC: Avi Kivity <avi@xxxxxxxxxx> --- v2: don't get rid of the actual values =) --- arch/x86/kvm/x86.c | 9 ++++++--- 1 files changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c39ab4a..5707405 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1151,15 +1151,18 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) vcpu->last_guest_tsc = tsc_timestamp; vcpu->hv_clock.flags = 0; + shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0); + /* * The interface expects us to write an even number signaling that the * update is finished. Since the guest won't see the intermediate - * state, we just increase by 2 at the end. + * state, we just increase by 2 at the end. We use the guest's value as + * a basis to make it migration-safe. */ + memcpy(&vcpu->hv_clock.version, shared_kaddr + vcpu->time_offset, + sizeof(vcpu->hv_clock.version)); vcpu->hv_clock.version += 2; - shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0); - memcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock, sizeof(vcpu->hv_clock)); -- 1.7.2.3 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
