linux-kernel - Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when L2 guest is running

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Message-ID: <6d2cd9ce-da0e-8b61-e3a9-78be3b32a6e4@redhat.com>
Date:	Wed, 6 Jul 2016 09:46:42 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <kernellwp@...il.com>, kvm <kvm@...r.kernel.org>,
	Radim Krcmar <rkrcmar@...hat.com>,
	Yunhong Jiang <yunhong.jiang@...el.com>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>
Subject: Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when
 L2 guest is running



On 06/07/2016 08:05, Haozhong Zhang wrote:
>> > 
>> > Nested preemption timer is emulated by hrtimer, so it doesn't
>> > influence vmcs02, why this is needed?
> Nested (L2) preemption timer is not affected for sure, and this patch
> is to fix another problem caused by using L1 preemption timer for L1
> TSC deadline timer. When we use L1 VMX preemption timer for L1 TSC
> deadline timer, we intend to use the pin-based exec config and the VMX
> preemption timer value in vmcs01. However, when L2 guest is running,
> vmcs02 is loaded as the current VMCS so that a different VMX
> preemption timer config is used (i.e. VMX preemption timer is disabled
> in prepare_vmcs02()). If we still use preemption timer for L1 TSC
> deadline timer at this moment, then L1 TSC deadline timer will not be
> able to be triggered when L2 guest is running.

The right fix then is to set the pin-based controls in prepare_vmcs02,
based on vcpu->arch.hv_deadline_tsc.

Paolo