Re: [Xen-devel] PVH and mtrr/PAT.........

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.11.13 at 13:16, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 22/11/13 11:09, Jan Beulich wrote:
>>>>> On 22.11.13 at 11:43, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>>> I'm not incredibly familiar with the PAT / MTRR stuff, either from a
>>> hardware level or a Xen level, so sorry if this is a dumb question. It
>>> sounds like you're saying, because we have virtual MTRRs that are
>>> already translated into EPT types, we should disable virtual MTRRs and
>>> use PAT instead.  That doesn't make any kind of sense to me.  (I didn't
>>> understand it when Jan said it either.)
>> The underlying observation is that MTRRs aren't really needed -
>> all they can do can be done with PAT. They pre-date PAT though,
>> hence hardware vendors can't easily drop them. But in a model
>> like PVH I just don't see the value of allowing their use, considering
>> that this adds unnecessary complexity.
> 
> OK -- so when we move forward with the plan of "PVH mode is HVM mode 
> with a couple of tweaks", you think that we should have an "enable 
> virtual MTRR" flag, and disable this for PVH mode?

Yes (provided the guest kernel code can be made cope with this).

Jan


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