linux-kernel - Re: [PATCH] KVM: LAPIC: Disarm LAPIC timer includes pending timer around TSC deadline switch

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Date:   Wed, 11 May 2022 10:42:32 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: LAPIC: Disarm LAPIC timer includes pending timer
 around TSC deadline switch

On Tue, 10 May 2022 at 21:43, Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Tue, May 10, 2022, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > The timer is disarmed when switching between TSC deadline and other modes,
> > however, the pending timer is still in-flight, so let's accurately set
> > everything to a disarmed state.
> >
> > Fixes: 4427593258 (KVM: x86: thoroughly disarm LAPIC timer around TSC deadline switch)
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  arch/x86/kvm/lapic.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> > index 66b0eb0bda94..0274d17d91c2 100644
> > --- a/arch/x86/kvm/lapic.c
> > +++ b/arch/x86/kvm/lapic.c
> > @@ -1562,6 +1562,7 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
> >                       kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> >                       apic->lapic_timer.period = 0;
> >                       apic->lapic_timer.tscdeadline = 0;
> > +                     atomic_set(&apic->lapic_timer.pending, 0);
>
> What about doing this in cancel_apic_timer()?  That seems to be a more natural
> place to clear pending.  It's somewhat redundant since the other two callers of
> cancel_apic_timer() start the timer immediately after, i.e. clear pending anyways,
> but IMO it's odd to leave pending set when canceling the timer.

Do it in v2.

    Wanpeng