linux-kernel - Re: [PATCH v3 2/3] KVM: MMU: fix accessed bit set on prefault path

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Message-ID: <20101130175005.GA2924@redhat.com>
Date:	Tue, 30 Nov 2010 19:50:05 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.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 v3 2/3] KVM: MMU: fix accessed bit set on prefault path

On Wed, Dec 01, 2010 at 12:52:22AM +0800, Xiao Guangrong wrote:
> On 11/30/2010 09:29 PM, Gleb Natapov wrote:
> 
> >> +	if (!shadow_accessed_mask)
> >> +		return;
> >> +
> > I don't get this. As far as I can see VMX inits shadow_accessed_mask to
> > be zero if ept is enabled. This line here means that we never prefault with ept
> > enabled. It is opposite from what it should be.
> > 
> 
> Since it's no accessed bit on EPT, it's no way to distinguish between actually
> accessed translations and prefault.
Why is this a problem? We do what this page to not be evicted again
since we expect it to be accessed.

--
			Gleb.
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