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

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Date:   Tue, 8 Jun 2021 18:27:15 +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 v2 2/3] KVM: LAPIC: Reset TMCCT during vCPU reset

On 07/06/21 09:19, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@...cent.com>
> 
> The value of the current counter register after reset is 0 for both
> Intel and AMD, let's do it in kvm, though, the TMCCT is always computed
> on-demand and never directly readable.

It's useless though since it's never read except by KVM_SET_LAPIC. 
Perhaps instead set TMCCT to 0 in kvm_apic_set_state, instead of keeping 
the value that was filled in by KVM_GET_LAPIC?

Paolo

> Reviewed-by: Jim Mattson <jmattson@...gle.com>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
> v1 -> v2:
>   * update patch description
> 
>   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 6d72d8f..cbfdecd 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2352,6 +2352,7 @@ void kvm_lapic_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	kvm_lapic_set_reg(apic, APIC_ICR2, 0);
>   	kvm_lapic_set_reg(apic, APIC_TDCR, 0);
>   	kvm_lapic_set_reg(apic, APIC_TMICT, 0);
> +	kvm_lapic_set_reg(apic, APIC_TMCCT, 0);
>   	for (i = 0; i < 8; i++) {
>   		kvm_lapic_set_reg(apic, APIC_IRR + 0x10 * i, 0);
>   		kvm_lapic_set_reg(apic, APIC_ISR + 0x10 * i, 0);
>