linux-kernel - Re: [PATCH v2 8/10] KVM: MMU: prefetch ptes when intercepted guest #PF

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Message-ID: <4C2A96AE.6020103@cn.fujitsu.com>
Date:	Wed, 30 Jun 2010 08:58:22 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 8/10] KVM: MMU: prefetch ptes when intercepted guest
 #PF



Marcelo Tosatti wrote:

>>> Also prefetch should be disabled for EPT, due to lack of accessed bit.
>>>
>> But we call mmu_set_spte() with speculative == false, it not touch the accessed bit.
> 
> There is no accessed bit on EPT. So the aging code (kvm_age_rmapp)
> considers any present translation as accessed. There is no way to
> distinguish between actually accessed translations and prefetched (but
> unused) ones.
> 

You are right, i'll disable the prefetch for EPT in the next version, thanks for
you point it out.
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