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RE: [Xen-devel] [PATCH] VGA acceleration utilizing shadowlogdirtyfunctio

To: "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>, "Huang, Xinmei" <xinmei.huang@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH] VGA acceleration utilizing shadowlogdirtyfunctionality
From: "Ian Pratt" <Ian.Pratt@xxxxxxxxxxxx>
Date: Fri, 18 May 2007 10:59:06 +0100
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Thread-topic: [Xen-devel] [PATCH] VGA acceleration utilizing shadowlogdirtyfunctionality
> xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote:
> > I think the most efficient way of accelerating the framebuffer scan
> > to use the dirty bits in the PTEs that map it. Typically, most
> > OSes will
> > use just a single set of PTEs for mapping the framebuffer, and
> > it should
> > be possible to scan these to fill out a bitmap of what's been
> I think we are saying shadow PTEs here, a potential problem here is
> the shadow PTEs may disappear for some reason like recycling etc.

That shouldn't happen too frequently. 

I think the easiest way of handling this is to return dirty status for
the PTEs we don't know about, and then reshadow the missing page so that
we'll know next time around.

We're only talking about a couple of pages here, so we're not going to
perturb all the shadow cache cleverness in any significant way.

> But we can walkaround this like:
>       Keep track of guest frame's dirty bitmap in hypervisor and
> update it
> if a dirty shadow PTE for VRAM is recycled. In this way we keep the
> info though a little bit ugly.

Lets try and keep it simple :)

> Is this what you want? BTW, Do u agree we can assume there is no
> multiple map of guest VRAM for now, othrewise the patch need more to



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