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

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Date:	Wed, 6 Jul 2016 08:04:09 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <kernellwp@...il.com>,
	Haozhong Zhang <haozhong.zhang@...el.com>
Cc:	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 07:37, Wanpeng Li wrote:
> Cc Jan,
> 2016-07-06 13:10 GMT+08:00 Haozhong Zhang <haozhong.zhang@...el.com>:
>> A different VMCS is loaded when L2 guest is running, so it's incorrect
>> to use the VMX preemption timer for L1 TSC deadline timer. This patch
>> switches to hrtimer for L1 TSC deadline timer when entering L2 guest,
>> and switches back to VMX preemption timer when nested VMEXIT from L2 to
>> L1.
> 
> Nested preemption timer is emulated by hrtimer, so it doesn't
> influence vmcs02, why this is needed?

I agree (and nested APIC timer is emulated by L1).  Because the L1 APIC
timer is set in the preemption timer before vmentry, this should not be
necessary.

Paolo