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

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Message-ID: <4C3C021E.1000709@redhat.com>
Date:	Tue, 13 Jul 2010 09:05:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.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()

On 07/13/2010 08:48 AM, Xiao Guangrong wrote:
>
>> 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.
>    

Oh yes.

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

Should be simple - disable prefetch for slots that have dirty tracking 
enabled.

What about the Linux accessed and dirty bits?  Need to instantiate the 
speculative sptes with accessed and dirty bits clear (and later examine 
them when we release the page).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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