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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Thu, 17 Jun 2021 12:33:09 +0800
Message-ID: <CANRm+CyO9yQk8KsNa8hKyTA3V9XnB41=roPcK8Vn0dzR7Ywktg@mail.gmail.com>
Subject: Re: [PATCH v3] KVM: LAPIC: Keep stored TMCCT register value 0 after KVM_SET_LAPIC
To:     LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
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kindly ping, :)
On Wed, 9 Jun 2021 at 15:17, Wanpeng Li <kernellwp@gmail.com> wrote:
>
> From: Wanpeng Li <wanpengli@tencent.com>
>
> 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 could store zero in
> vcpu->arch.apic->regs after it uses it, and then the stored value would
> always be zero. In addition, the TMCCT is always computed on-demand and
> never directly readable.
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.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 6d72d8f43310..9bd29b3ca790 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2628,6 +2628,7 @@ int kvm_apic_set_state(struct kvm_vcpu *vcpu, struct kvm_lapic_state *s)
>         apic_manage_nmi_watchdog(apic, kvm_lapic_get_reg(apic, APIC_LVT0));
>         update_divide_count(apic);
>         __start_apic_timer(apic, APIC_TMCCT);
> +       kvm_lapic_set_reg(apic, APIC_TMCCT, 0);
>         kvm_apic_update_apicv(vcpu);
>         apic->highest_isr_cache = -1;
>         if (vcpu->arch.apicv_active) {
> --
> 2.25.1
>