commit 72cbc8f04f upstream.
After commit ID in the Fixes: tag, pat_enabled() returns false (because
of PAT initialization being suppressed in the absence of MTRRs being
announced to be available).
This has become a problem: the i915 driver now fails to initialize when
running PV on Xen (i915_gem_object_pin_map() is where I located the
induced failure), and its error handling is flaky enough to (at least
sometimes) result in a hung system.
Yet even beyond that problem the keying of the use of WC mappings to
pat_enabled() (see arch_can_pci_mmap_wc()) means that in particular
graphics frame buffer accesses would have been quite a bit less optimal
than possible.
Arrange for the function to return true in such environments, without
undermining the rest of PAT MSR management logic considering PAT to be
disabled: specifically, no writes to the PAT MSR should occur.
For the new boolean to live in .init.data, init_cache_modes() also needs
moving to .init.text (where it could/should have lived already before).
[ bp: This is the "small fix" variant for stable. It'll get replaced
with a proper PAT and MTRR detection split upstream but that is too
involved for a stable backport.
- additional touchups to commit msg. Use cpu_feature_enabled(). ]
Fixes: bdd8b6c982 ("drm/i915: replace X86_FEATURE_PAT with pat_enabled()")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Cc: Juergen Gross <jgross@suse.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/9385fa60-fa5d-f559-a137-6608408f88b0@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
a210408b90