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Re: [Xen-devel] mapping of memory below 16Mb

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Thu, 24 Jan 2008 16:27:14 +0000
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 24 Jan 2008 08:28:00 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AchepfouOLhgMMqZEdy57QAX8io7RQ==
  • Thread-topic: [Xen-devel] mapping of memory below 16Mb

On 24/1/08 16:24, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>>> The WP attribute raises another question: Are there any plans to make
>>> Xen use PAT rather than (relying on) MTRRs? Linux folks seem to be
>>> finally getting closer to this, too, so even virtual PAT support may be
>>> needed in not too distant future...
>> We already support PAT for both PV guests and HVM guests.
> Oh, and my understanding of PAT support goes beyond just setting the
> PAT MSR and adjusting page table flags. Specifically, if we have PAT we
> should never need to modify MTRRs, which would eliminate conflicts on
> updates of those that I'm seeing on various boxes, always just
> depending on how BIOS sets them up, and always related to overlaps
> of the video memory with existing MTRR ranges.

That's a dom0 issue. Xen itself does not proactively mess with the MTRRs.

 -- Keir

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