Re: [PATCH 2/2] x86/pat: add functions to query specific cache mode availability

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 5/19/22 10:15 PM, Chuck Zmudzinski wrote:
> On 5/3/22 9:22 AM, Juergen Gross wrote:
> > Some drivers are using pat_enabled() in order to test availability of
> > special caching modes (WC and UC-). This will lead to false negatives
> > in case the system was booted e.g. with the "nopat" variant and the
> > BIOS did setup the PAT MSR supporting the queried mode, or if the
> > system is running as a Xen PV guest.
> Hello,
>
> I am also getting a false positive
Sorry, I meant false negative here, not false
positive.

Chuck

> in a Xen Dom0 from
> pat_enabled() where bdd8b6c98239 patched the file
>
> drivers/gpu/drm/i915/gem/i915_gem_pages.c
>
> I think this patch also needs to touch that file to
> fix the issue I am seeing.
...