linux-kernel - Re: [PATCH v2 2/3] KVM: LAPIC: Reset TMCCT during vCPU reset

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Message-ID: <f8c80e8a-0749-eb5b-d5ab-162f504c9d33@redhat.com>
Date:   Wed, 9 Jun 2021 07:51:54 +0200
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 <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 2/3] KVM: LAPIC: Reset TMCCT during vCPU reset

On 09/06/21 04:15, Wanpeng Li wrote:
> On Wed, 9 Jun 2021 at 00:27, Paolo Bonzini <pbonzini@...hat.com> wrote:
> [...]
>> Perhaps instead set TMCCT to 0 in kvm_apic_set_state, instead of keeping
>> the value that was filled in by KVM_GET_LAPIC?
> 
> Keeping the value that was filled in by KVM_GET_LAPIC is introduced by
> commit 24647e0a39b6 (KVM: x86: Return updated timer current count
> register from KVM_GET_LAPIC), could you elaborate more? :)

KVM_GET_LAPIC stores the current value of TMCCT and KVM_SET_LAPIC's 
memcpy stores it in vcpu->arch.apic->regs.  KVM_SET_LAPIC perhaps could 
store zero in vcpu->arch.apic->regs after it uses it, and then the 
stored value would always be zero.

Paolo