From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wanpeng Li Subject: Re: [PATCH] KVM: x86: pvclock: Handle first-time write to pvclock-page contains random junk Date: Mon, 13 Nov 2017 08:40:01 +0800 Message-ID: References: <1509891090-8985-1-git-send-email-liran.alon@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Paolo Bonzini , Radim Krcmar , kvm , idan.brown@oracle.com, Konrad Rzeszutek Wilk To: Liran Alon Return-path: Received: from mail-ot0-f196.google.com ([74.125.82.196]:54667 "EHLO mail-ot0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132AbdKMAkC (ORCPT ); Sun, 12 Nov 2017 19:40:02 -0500 Received: by mail-ot0-f196.google.com with SMTP id w8so12346570otw.11 for ; Sun, 12 Nov 2017 16:40:01 -0800 (PST) In-Reply-To: <1509891090-8985-1-git-send-email-liran.alon@oracle.com> Sender: kvm-owner@vger.kernel.org List-ID: 2017-11-05 22:11 GMT+08:00 Liran Alon : > 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 KVM does, please refer to memset(hv_clock, 0, size) in kvmclock_init(). Regards, Wanpeng Li > 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 > Reviewed-by: Nikita Leshenko > Reviewed-by: Konrad Rzeszutek Wilk > Signed-off-by: Konrad Rzeszutek Wilk > --- > 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, > -- > 1.9.1 >