On Wed, Feb 2, 2011 at 10:51 AM, Glauber Costa <glommer@xxxxxxxxxx> wrote: > 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: > > Âvcpu->arch.hv_clock.version is initialized to zero. > ÂGuest reads version (result: 2) > ÂGuest starts reading data > ÂLive migration; vcpu->arch.hv_clock.version is zeroed > ÂSteal time update; vcpu->arch.hv_clock.version += 2; write to guest > ÂGuest continues reading data > ÂGuest reads version (result: 2) Please ignore it. I did test this patch but appearently used the wrong module, and it tricked me this version is obviously wrong. > > Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx> > CC: Avi Kivity <avi@xxxxxxxxxx> > --- > Âarch/x86/kvm/x86.c | Â Â9 ++++++--- > Â1 files changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index c39ab4a..7fdc84a 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) > Â Â Â Âvcpu->last_guest_tsc = tsc_timestamp; > Â Â Â Âvcpu->hv_clock.flags = 0; > > + Â Â Â shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0); > + > Â Â Â Â/* > Â Â Â Â * The interface expects us to write an even number signaling that the > Â Â Â Â * update is finished. Since the guest won't see the intermediate > - Â Â Â Â* state, we just increase by 2 at the end. > + Â Â Â Â* state, we just increase by 2 at the end. We use the guest's value as > + Â Â Â Â* a basis to make it migration-safe. > Â Â Â Â */ > + Â Â Â memcpy(&vcpu->hv_clock, shared_kaddr + vcpu->time_offset, > + Â Â Â Â Â Â Âsizeof(vcpu->hv_clock)); > Â Â Â Âvcpu->hv_clock.version += 2; > > - Â Â Â shared_kaddr = kmap_atomic(vcpu->time_page, KM_USER0); > - > Â Â Â Âmemcpy(shared_kaddr + vcpu->time_offset, &vcpu->hv_clock, > Â Â Â Â Â Â Â sizeof(vcpu->hv_clock)); > > -- > 1.7.2.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at Âhttp://vger.kernel.org/majordomo-info.html > Please read the FAQ at Âhttp://www.tux.org/lkml/ > -- Sent from my Atari. -- 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
