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Message-ID: <48D2D3B2.10503@goop.org>
Date: Thu, 18 Sep 2008 15:18:26 -0700
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: Avi Kivity <avi@...hat.com>
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>,
Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: Populating multiple ptes at fault time
Avi Kivity wrote:
>> Do you need to set the A bit synchronously?
>
> Yes, of course (if no guest cooperation).
Is the A bit architecturally guaranteed to be synchronously set? Can
speculative accesses set it? SDM vol 3 is a bit vague about it.
> I'll fail my own unit tests.
>
> If we add an async mode for guests that can cope, maybe this is
> workable. I guess this is what you're suggesting.
>
Yes. At worst Linux would underestimate the process RSS a bit
(depending on how many unsynchronized ptes you leave lying around). I
bet there's an appropriate pvop hook you could use to force
synchronization just before the kernel actually inspects the bits
(leaving lazy mode sounds good).
J
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