On 05/11/2017 15:11, Liran Alon wrote: > When guest passes KVM it's pvclock-page GPA via WRMSR to > MSR_KVM_SYSTEM_TIME / MSR_KVM_SYSTEM_TIME_NEW, KVM don't initialize > pvclock-page to some start-values. It just requests a clock-update which > will happen before entering to guest. > > The clock-update logic will call kvm_setup_pvclock_page() to update the > pvclock-page with info. However, kvm_setup_pvclock_page() *wrongly* > assumes that the version-field is initialized to an even number. This is > wrong because at first-time write, field could be any-value. > > Fix simply makes sure that if first-time version-field is odd, increment > it once more to make it even and only then start standard logic. > This follows same logic as done in other pvclock shared-pages (See > kvm_write_wall_clock() and record_steal_time()). > > Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx> > Reviewed-by: Nikita Leshenko <nikita.leshchenko@xxxxxxxxxx> > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > --- > arch/x86/kvm/x86.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 03869eb7fcd6..181106080e41 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1830,6 +1830,9 @@ static void kvm_setup_pvclock_page(struct kvm_vcpu *v) > */ > BUILD_BUG_ON(offsetof(struct pvclock_vcpu_time_info, version) != 0); > > + if (guest_hv_clock.version & 1) > + ++guest_hv_clock.version; /* first time write, random junk */ > + > vcpu->hv_clock.version = guest_hv_clock.version + 1; > kvm_write_guest_cached(v->kvm, &vcpu->pv_time, > &vcpu->hv_clock, > Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx