Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr

H. Peter Anvin
2010-09-28T18:19:55Z

On 09/28/2010 11:13 AM, Jeremy Fitzhardinge wrote:
> On 09/28/2010 10:56 AM, H. Peter Anvin wrote:
>> On 09/28/2010 10:13 AM, Jeremy Fitzhardinge wrote:
>>> Yes, we could just mask out the MTRR CPU feature and rely entirely on PAT.
>>>
>>> The alternative would be to use the wrmsr hooks to emulate the Intel
>>> MTRR registers by mapping them to hypercalls, but that seems needlessly
>>> complex.
>>>
>> Indeed. Relying on pure PAT is the Right Thing[TM].
>
> Is there a plan to formally deprecate /proc/mtrr and the kernel
> infrastructure behind it?
>

No, and we really can't do it for a couple of reasons:

a) Pre-PAT hardware;
b) MTRRs and PAT interact on hardware;
c) MTRRs, but not PAT, interact with SMM.

However, since a virtual machine like Xen doesn't have these issues, it
doesn't apply.

-hpa