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 14:02:08 -0300 [thread overview]
Message-ID: <20210318170208.GB36190@fuller.cnet> (raw)
In-Reply-To: <20210316143736.964151-3-vkuznets@redhat.com>
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...
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 17:33 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 [this message]
2021-03-18 18:04 ` Marcelo Tosatti
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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