linux-kernel - Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch and pte prefetch

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Date:	Wed, 7 Jul 2010 12:30:18 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v5 8/9] KVM: MMU: combine guest pte read between fetch
 and pte prefetch

On Wed, Jul 07, 2010 at 10:10:04PM +0800, Xiao Guangrong wrote:
> 
> 
> Marcelo Tosatti wrote:
> 
> >>>>
> >>>> It reads the 16 aligned items around sptep's corresponding gpte and this gpte
> >>>> is also in this area. :-)
> >>> But you removed that in patch 8?
> >>>
> >> Oh, i just want it good for review, you mean it's better let patch 7 and 8 in one patch?
> > 
> > I mean patch 7 is wrong because it removes rereading of gpte, with
> > mmu_lock held, in the prefetch patch.
> > 
> 
> Marcelo,
> 
> Sorry, i don't understand it clearly.
> 
> In the patch 7, we read gpte like this:
> 
> 	hold mmu_lock
> 	atomic read gpte during guest mapping's checking in 'fetch' path
> 	atomic read 16 aligned items chunk (include gpte) in pte_prefetch path
> 	release mmu_lock
> 
> And in the patch 8, we do it like this:
> 	hold mmu_lock
> 
> 	atomic read 16 aligned items chunk (include gpte) in 'fetch' path, and
>         saved this chunk to gw->prefetch_ptes
> 	
>         get gptes form gw->prefetch_ptes in pte_prefetch path
> 
> 	release mmu_lock
> 
> Could you please tell me where is wrong?

You're right. Patchset looks good to me.

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