linux-kernel - Re: [PATCH 1/2] KVM: LAPIC: write 0 to TMICT should also cancel vmx-preemption timer

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Message-ID: <YLpIni1VKYYfUE8D@google.com>
Date:   Fri, 4 Jun 2021 15:37:02 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Wanpeng Li <kernellwp@...il.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 1/2] KVM: LAPIC: write 0 to TMICT should also cancel
 vmx-preemption timer

On Fri, Jun 04, 2021, Wanpeng Li wrote:
> On Thu, 3 Jun 2021 at 23:20, Sean Christopherson <seanjc@...gle.com> wrote:
> >
> > On Thu, Jun 03, 2021, Wanpeng Li wrote:
> > > From: Wanpeng Li <wanpengli@...cent.com>
> > >
> > > According to the SDM 10.5.4.1:
> > >
> > >   A write of 0 to the initial-count register effectively stops the local
> > >   APIC timer, in both one-shot and periodic mode.
> > >
> > > The lapic timer oneshot/periodic mode which is emulated by vmx-preemption
> > > timer doesn't stop since vmx->hv_deadline_tsc is still set.
> >
> > But the VMX preemption timer is only used for deadline, never for oneshot or
> > periodic.  Am I missing something?
> 
> Yes, it is upstream.

Huh.  I always thought 'tscdeadline' alluded to the timer being in deadline mode
and never looked closely at the arming code.  Thanks!

Maybe name the new helper cancel_apic_timer() to align with start_apic_timer()
and restart_apic_timer()?  With that:

Reviewed-by: Sean Christopherson <seanjc@...gle.com>