linux-kernel - Re: Populating multiple ptes at fault time

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Message-ID: <48D17E75.80807@redhat.com>
Date:	Wed, 17 Sep 2008 15:02:29 -0700
From:	Avi Kivity <avi@...hat.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Nick Piggin <nickpiggin@...oo.com.au>,
	Hugh Dickens <hugh@...itas.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...ranet.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: Populating multiple ptes at fault time

Jeremy Fitzhardinge wrote:
> Minor faults are easier; if the page already exists in memory, we should
> just create mappings to it.  If neighbouring pages are also already
> present, then we can can cheaply create mappings for them too.
>
>   

One problem is the accessed bit.  If it's unset, the shadow code cannot 
make the pte present (since it has to trap in order to set the accessed 
bit); if it's set, we're lying to the vm.

This doesn't affect Xen, only kvm.

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

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