linux-kernel - Re: [PATCH] KVM: LAPIC: Also cancel preemption timer when disarm LAPIC timer

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Date:   Thu, 26 Mar 2020 08:20:42 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.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: Also cancel preemption timer when disarm
 LAPIC timer

On Wed, 25 Mar 2020 at 23:55, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 24/03/20 07:32, Wanpeng Li wrote:
> >                       hrtimer_cancel(&apic->lapic_timer.timer);
> > +                     preempt_disable();
> > +                     if (apic->lapic_timer.hv_timer_in_use)
> > +                             cancel_hv_timer(apic);
> > +                     preempt_enable();
> >                       kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> >                       apic->lapic_timer.period = 0;
> >                       apic->lapic_timer.tscdeadline = 0;
>
> There are a few other occurrences of hrtimer_cancel, and all of them
> probably have a similar issue.  What about adding a cancel_apic_timer

Other places are a little different, here we just disarm the timer,
other places we will restart the timer just after the disarm except
the vCPU reset (fixed in commit 95c065400a1 (KVM: VMX: Stop the
preemption timer during vCPU reset)), the restart will override
vmx->hv_deadline_tsc. What do you think? I can do it if introduce
cancel_apic_timer() is still better.

    Wanpeng