linux-kernel - Re: [PATCH v3] KVM: LAPIC: Keep stored TMCCT register value 0 after KVM_SET

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Message-ID: <02391363-6713-1548-fa4b-70b70cc96f79@redhat.com>
Date:   Thu, 17 Jun 2021 20:26:15 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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 v3] KVM: LAPIC: Keep stored TMCCT register value 0 after
 KVM_SET_LAPIC

On 09/06/21 09:16, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.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@...hat.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.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) {
> 

Queued, thanks.

Paolo