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

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Date:   Thu, 26 Mar 2020 01:28:03 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.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 26/03/20 01:20, Wanpeng Li wrote:
>> 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.

At least start_apic_timer() would benefit from adding hrtimer_cancel(),
removing it from kvm_set_lapic_tscdeadline_msr and kvm_lapic_reg_write.
 But you're right that it doesn't benefit from a cancel_apic_timer(),
because ultimately they either update the preemption timer or cancel it
in start_sw_timer.  So I'll apply your patch and send a cleanup myself
for start_apic_timer.

Thanks,

Paolo