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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 24/1/08 15:57, "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.
> 
> Hmm, I must have missed this going in. Is the indexing into PAT then
> considered part of the ABI (as I can't see either a hypercall a guest
> could use to learn what bit combination to use for certain attributes or
> one to set a virtual PAT value)?

Xen statically initialises the PAT MSR to 0x0000050100070406 and that is
part of the PV guest ABI. PAT6 and PAT7 indexes are reserved -- their memory
type may change in future.

> And regardless of that, SVM code has no sign of handling accesses to the
> PAT MSR.

Oh, some VMX code needs to be common-ised then. But since this only makes
any difference for guests with direct hardware passthru, and that doesn't
work on AMD systems yet, this is hardly a priority.

 -- Keir



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel