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Subject: Re: [PATCH v2 1/3] KVM: LAPIC: Write 0 to TMICT should also cancel
 vmx-preemption timer
To:     Wanpeng Li <kernellwp@gmail.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc:     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>
References: <1623050385-100988-1-git-send-email-wanpengli@tencent.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <9a95474c-5430-83d5-db65-2909191bd9f5@redhat.com>
Date:   Tue, 8 Jun 2021 18:27:45 +0200
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On 07/06/21 09:19, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
> According to the SDM 10.5.4.1:
> 
>    A write of 0 to the initial-count register effectively stops the local
>    APIC timer, in both one-shot and periodic mode.
> 
> However, the lapic timer oneshot/periodic mode which is emulated by vmx-preemption
> timer doesn't stop by writing 0 to TMICT since vmx->hv_deadline_tsc is still
> programmed and the guest will receive the spurious timer interrupt later. This
> patch fixes it by also cancelling the vmx-preemption timer when writing 0 to
> the initial-count register.
> 
> Reviewed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v1 -> v2:
>   * rename to cancel_apic_timer
>   * update patch description
> 
>   arch/x86/kvm/lapic.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 8120e86..6d72d8f 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1494,6 +1494,15 @@ static void limit_periodic_timer_frequency(struct kvm_lapic *apic)
>   
>   static void cancel_hv_timer(struct kvm_lapic *apic);
>   
> +static void cancel_apic_timer(struct kvm_lapic *apic)
> +{
> +	hrtimer_cancel(&apic->lapic_timer.timer);
> +	preempt_disable();
> +	if (apic->lapic_timer.hv_timer_in_use)
> +		cancel_hv_timer(apic);
> +	preempt_enable();
> +}
> +
>   static void apic_update_lvtt(struct kvm_lapic *apic)
>   {
>   	u32 timer_mode = kvm_lapic_get_reg(apic, APIC_LVTT) &
> @@ -1502,11 +1511,7 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
>   	if (apic->lapic_timer.timer_mode != timer_mode) {
>   		if (apic_lvtt_tscdeadline(apic) != (timer_mode ==
>   				APIC_LVT_TIMER_TSCDEADLINE)) {
> -			hrtimer_cancel(&apic->lapic_timer.timer);
> -			preempt_disable();
> -			if (apic->lapic_timer.hv_timer_in_use)
> -				cancel_hv_timer(apic);
> -			preempt_enable();
> +			cancel_apic_timer(apic);
>   			kvm_lapic_set_reg(apic, APIC_TMICT, 0);
>   			apic->lapic_timer.period = 0;
>   			apic->lapic_timer.tscdeadline = 0;
> @@ -2092,7 +2097,7 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>   		if (apic_lvtt_tscdeadline(apic))
>   			break;
>   
> -		hrtimer_cancel(&apic->lapic_timer.timer);
> +		cancel_apic_timer(apic);
>   		kvm_lapic_set_reg(apic, APIC_TMICT, val);
>   		start_apic_timer(apic);
>   		break;
> 

Queued this one, thanks.

Paolo