linux-kernel - Re: [PATCH 5/8] KVM: don't touch vcpu stat after async pf is complete

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Message-ID: <4CC927B1.2020807@cn.fujitsu.com>
Date:	Thu, 28 Oct 2010 15:35:13 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 5/8] KVM: don't touch vcpu stat after async pf is complete

On 10/27/2010 06:44 PM, Gleb Natapov wrote:
> On Wed, Oct 27, 2010 at 05:05:57PM +0800, Xiao Guangrong wrote:
>> Don't make a KVM_REQ_UNHALT request after async pf is completed since it
>> can break guest's 'halt' instruction.
>>
> Why is it a problem? CPU may be unhalted by different events so OS
> shouldn't depend on it.
> 

We don't know how guest OS handles it after HLT instruction is completed,
according to X86's spec, only NMI/INTR/RESET/INIT/SMI can break halt state,
it violations the hardware behavior if we allow other event break this
state. Your opinion? :-)
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