linux-kernel - Re: [PATCH] KVM: LAPIC: Also cancel preemption timer when disarm LAPIC timer

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Message-ID: <87imit7p36.fsf@vitty.brq.redhat.com>
Date:   Tue, 24 Mar 2020 16:24:45 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: LAPIC: Also cancel preemption timer when disarm LAPIC timer

Wanpeng Li <kernellwp@...il.com> writes:

> From: Wanpeng Li <wanpengli@...cent.com>
>
> The timer is disarmed when switching between TSC deadline and other modes, 
> we should set everything to disarmed state, however, LAPIC timer can be 
> emulated by preemption timer, it still works if vmx->hv_deadline_timer is 
> not -1. This patch also cancels preemption timer when disarm LAPIC timer.
>
> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> ---
>  arch/x86/kvm/lapic.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 338de38..a38f1a8 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1445,6 +1445,8 @@ static void limit_periodic_timer_frequency(struct kvm_lapic *apic)
>  	}
>  }
>  
> +static void cancel_hv_timer(struct kvm_lapic *apic);
> +

Nitpick: cancel_hv_timer() is only 4 lines long so I'd suggest we move
it instead of adding a forward declaration.

>  static void apic_update_lvtt(struct kvm_lapic *apic)
>  {
>  	u32 timer_mode = kvm_lapic_get_reg(apic, APIC_LVTT) &
> @@ -1454,6 +1456,10 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
>  		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();
>  			kvm_lapic_set_reg(apic, APIC_TMICT, 0);
>  			apic->lapic_timer.period = 0;
>  			apic->lapic_timer.tscdeadline = 0;

-- 
Vitaly