From: Sean Christopherson <seanjc@google.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH] KVM: LAPIC: Advancing the timer expiration on guest initiated write
Date: Wed, 3 Mar 2021 08:12:43 -0800 [thread overview]
Message-ID: <YD+1e1iLyKKWL8FX@google.com> (raw)
In-Reply-To: <CANRm+Cy_rNAai+u5pyBXKmQP_Qp=3e_hwi2g9bAFMiocCpru1A@mail.gmail.com>
On Wed, Mar 03, 2021, Wanpeng Li wrote:
> > Side topic, I think there's a theoretical bug where KVM could inject a spurious
> > timer interrupt. If KVM is using hrtimer, the hrtimer expires early due to an
> > overzealous timer_advance_ns, and the guest writes MSR_TSCDEADLINE after the
> > hrtimer expires but before the vCPU is kicked, then KVM will inject a spurious
> > timer IRQ since the premature expiration should have been canceled by the guest's
> > WRMSR.
> >
> > It could also cause KVM to soft hang the guest if the new lapic_timer.tscdeadline
> > is written before apic_timer_expired() captures it in expired_tscdeadline. In
> > that case, KVM will wait for the new deadline, which could be far in the future.
>
> The hrtimer_cancel() before setting new lapic_timer.tscdeadline in
> kvm_set_lapic_tscdeadline_msr() will wait for the hrtimer callback
> function to finish. Could it solve this issue?
Aha! Yep, that prevents my theoretical bug. Thanks!
prev parent reply other threads:[~2021-03-04 0:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 9:43 [PATCH] KVM: LAPIC: Advancing the timer expiration on guest initiated write Wanpeng Li
2021-03-02 17:16 ` Sean Christopherson
2021-03-03 1:13 ` Wanpeng Li
2021-03-03 16:12 ` Sean Christopherson [this message]
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