Re: [PATCH 1/2] KVM: LAPIC: write 0 to TMICT should also cancel vmx-preemption timer

From: Sean Christopherson <seanjc@google.com>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH 1/2] KVM: LAPIC: write 0 to TMICT should also cancel vmx-preemption timer
Date: Thu, 3 Jun 2021 15:20:07 +0000	[thread overview]
Message-ID: <YLjzJ59HPqGfhhvm@google.com> (raw)
In-Reply-To: <1622710841-76604-1-git-send-email-wanpengli@tencent.com>

On Thu, Jun 03, 2021, 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.
> 
> The lapic timer oneshot/periodic mode which is emulated by vmx-preemption 
> timer doesn't stop since vmx->hv_deadline_tsc is still set.

But the VMX preemption timer is only used for deadline, never for oneshot or
periodic.  Am I missing something?

static bool start_hv_timer(struct kvm_lapic *apic)
{
	struct kvm_timer *ktimer = &apic->lapic_timer;
	struct kvm_vcpu *vcpu = apic->vcpu;
	bool expired;

	WARN_ON(preemptible());
	if (!kvm_can_use_hv_timer(vcpu))
		return false;

	if (!ktimer->tscdeadline)  <-------
		return false;

	...
}