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

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Date:	Fri, 19 Sep 2008 10:45:03 -0700
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	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

On Wed, 2008-09-17 at 15:02 -0700, Avi Kivity wrote:
> 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.

Other archs too. On powerpc, !accessed -> not hashed (or not in the TLB
for SW loaded TLB platforms). 

Ben.


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