From: Marcelo Tosatti <mtosatti@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH v2 2/4] KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs
Date: Thu, 18 Mar 2021 15:04:46 -0300 [thread overview]
Message-ID: <20210318180446.GA41953@fuller.cnet> (raw)
In-Reply-To: <20210318170208.GB36190@fuller.cnet>
On Thu, Mar 18, 2021 at 02:02:08PM -0300, Marcelo Tosatti wrote:
> On Tue, Mar 16, 2021 at 03:37:34PM +0100, 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.
> >
> > Invalidate TSC page in kvm_gen_update_masterclock() to switch all vCPUs
> > to using MSR based clocksource (HV_X64_MSR_TIME_REF_COUNT).
>
> Hi Vitaly,
>
> Not clear why this is necessary, if the choice was to not touch TSC page
> at all, when invariant TSC is supported on the host...
s/invariant TSC/TSC scaling/
> Ah, OK, this is not for the migration with iTSC on destination case,
> but any call to kvm_gen_update_masterclock, correct?
next prev parent reply other threads:[~2021-03-18 18:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 14:37 [PATCH v2 0/4] KVM: x86: hyper-v: TSC page fixes Vitaly Kuznetsov
2021-03-16 14:37 ` [PATCH v2 1/4] KVM: x86: hyper-v: Limit guest to writing zero to HV_X64_MSR_TSC_EMULATION_STATUS Vitaly Kuznetsov
2021-03-16 14:37 ` [PATCH v2 2/4] KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs Vitaly Kuznetsov
2021-03-18 17:02 ` Marcelo Tosatti
2021-03-18 18:04 ` Marcelo Tosatti [this message]
2021-03-18 18:05 ` Paolo Bonzini
2021-03-18 18:30 ` Marcelo Tosatti
2021-03-19 9:29 ` Vitaly Kuznetsov
2021-03-16 14:37 ` [PATCH v2 3/4] KVM: x86: hyper-v: Track Hyper-V TSC page status Vitaly Kuznetsov
2021-03-17 8:07 ` Paolo Bonzini
2021-03-17 11:19 ` [PATCH v2 5/4] KVM: x86: hyper-v: Briefly document enum hv_tsc_page_status Vitaly Kuznetsov
2021-03-16 14:37 ` [PATCH v2 4/4] KVM: x86: hyper-v: Don't touch TSC page values when guest opted for re-enlightenment Vitaly Kuznetsov
2021-03-18 14:09 ` [PATCH v2 6/4] selftests: kvm: Add basic Hyper-V clocksources tests Vitaly Kuznetsov
2021-03-18 14:26 ` Paolo Bonzini
2021-03-18 14:52 ` Vitaly Kuznetsov
2021-03-18 15:01 ` Paolo Bonzini
2021-03-18 15:23 ` Vitaly Kuznetsov
2021-03-18 15:27 ` Paolo Bonzini
2021-03-18 16:57 ` Marcelo Tosatti
2021-03-18 17:50 ` Paolo Bonzini
2021-03-18 17:55 ` Marcelo Tosatti
2021-03-19 9:35 ` Vitaly Kuznetsov
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