From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Marcelo Tosatti <mtosatti@redhat.com>
Subject: Re: [PATCH 3/4] KVM: x86: hyper-v: Track Hyper-V TSC page status
Date: Tue, 16 Mar 2021 08:20:43 -0700 [thread overview]
Message-ID: <YFDMy9ghurF4pwuh@google.com> (raw)
In-Reply-To: <87a6r38exq.fsf@vitty.brq.redhat.com>
On Tue, Mar 16, 2021, Vitaly Kuznetsov wrote:
> Vitaly Kuznetsov <vkuznets@redhat.com> writes:
>
> > Sean Christopherson <seanjc@google.com> writes:
> >
> >> On Mon, Mar 15, 2021, Vitaly Kuznetsov wrote:
> >>> @@ -1193,8 +1199,13 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data,
> >>> }
> >>> case HV_X64_MSR_REFERENCE_TSC:
> >>> hv->hv_tsc_page = data;
> >>> - if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)
> >>> + if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) {
> >>> + if (!host)
> >>> + hv->hv_tsc_page_status = HV_TSC_PAGE_GUEST_CHANGED;
> >>> + else
> >>> + hv->hv_tsc_page_status = HV_TSC_PAGE_HOST_CHANGED;
> >>
> >> Writing the status without taking hv->hv_lock could cause the update to be lost,
> >> e.g. if a different vCPU fails kvm_hv_setup_tsc_page() at the same time, its
> >> write to set status to HV_TSC_PAGE_BROKEN would race with this write.
> >>
> >
> > Oh, right you are, the lock was somewhere in my brain :-) Will do in
> > v2.
>
> Actually no, kvm_hv_set_msr_pw() is only called from
> kvm_hv_set_msr_common() with hv->hv_lock held so we're already
> synchronized.
>
> ... and of course I figured that our by putting another
> mutex_lock()/mutex_unlock() here and then wondering why everything hangs
> :-)
Doh, sorry :-/
next prev parent reply other threads:[~2021-03-16 15:21 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-15 14:37 [PATCH 0/4] KVM: x86: hyper-v: TSC page fixes Vitaly Kuznetsov
2021-03-15 14:37 ` [PATCH 1/4] KVM: x86: hyper-v: Limit guest to writing zero to HV_X64_MSR_TSC_EMULATION_STATUS Vitaly Kuznetsov
2021-03-15 14:37 ` [PATCH 2/4] KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs Vitaly Kuznetsov
2021-03-15 15:45 ` Paolo Bonzini
2021-03-15 15:55 ` Vitaly Kuznetsov
2021-03-15 16:23 ` Paolo Bonzini
2021-03-16 12:29 ` Vitaly Kuznetsov
2021-03-15 14:37 ` [PATCH 3/4] KVM: x86: hyper-v: Track Hyper-V TSC page status Vitaly Kuznetsov
2021-03-15 15:15 ` Sean Christopherson
2021-03-15 15:34 ` Vitaly Kuznetsov
2021-03-16 12:24 ` Vitaly Kuznetsov
2021-03-16 15:20 ` Sean Christopherson [this message]
2021-03-15 14:37 ` [PATCH 4/4] KVM: x86: hyper-v: Don't touch TSC page values when guest opted for re-enlightenment Vitaly Kuznetsov
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