linux-kernel - Re: [PATCH v5 6/9] KVM: MMU: introduce pte_prefetch_topup_memory

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Message-ID: <4C3BFE12.4060009@cn.fujitsu.com>
Date:	Tue, 13 Jul 2010 13:48:02 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 6/9] KVM: MMU: introduce pte_prefetch_topup_memory_cache()



Avi Kivity wrote:
> On 07/13/2010 07:25 AM, Xiao Guangrong wrote:
>>
>>> Regressions? no.  Or do you mean the problem already exists?  Where?
>>>      
>> I mean this is a exist problem, likes invlpg, pte-write and sync-page,
>> there are
>> speculative path that it's not real access, but marked dirty if pte is
>> writable.
>>    
> 
> Right.  We should fix those too.
> 
> Prefetch is much more worrying though, especially with ept.  If a guest
> is using just 1/8 of the pages, it can look to migration as if it's
> using 100% of the pages.  The impact can be pretty large.

We disabled prefetch if ept is enabled since it can break access bit tracking.

I'll fix the dirty bit tracking before post the new version of this patchset.
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