On 15/03/21 15:37, Vitaly Kuznetsov wrote:
When KVM_REQ_MASTERCLOCK_UPDATE request is issued (e.g. after migration) we need to make sure no vCPU sees stale values in PV clock structures and thus all vCPUs are kicked with KVM_REQ_CLOCK_UPDATE. Hyper-V TSC page clocksource is global and kvm_guest_time_update() only updates in on vCPU0 but this is not entirely correct: nothing blocks some other vCPU from entering the guest before we finish the update on CPU0 and it can read stale values from the page. Call kvm_hv_setup_tsc_page() on all vCPUs. Normally, KVM_REQ_CLOCK_UPDATE should be very rare so we may not care much about being wasteful.
I think we should instead write 0 to the page in kvm_gen_update_masterclock. Paolo
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> --- arch/x86/kvm/x86.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 47e021bdcc94..882c509bfc86 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -2748,8 +2748,9 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) offsetof(struct compat_vcpu_info, time)); if (vcpu->xen.vcpu_time_info_set) kvm_setup_pvclock_page(v, &vcpu->xen.vcpu_time_info_cache, 0); - if (v == kvm_get_vcpu(v->kvm, 0)) - kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); + + kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock); + return 0; }
