[PATCH 0/6] Enhance PAT init to fix Xorg crashes

[Toshi Kani]

A Xorg failure on qemu32 was reported as a regression caused
by 'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is
disabled")'. [1] This patch-set fixes the regression.

Negative effects of this regression were two failures in Xorg
on qemu32 env, which were triggered by the fact that its virtual
CPU does not support MTRR. [2]
 #1. copy_process() failed in the check in reserve_pfn_range()
 #2. error path in copy_process() then hit WARN_ON_ONCE in
     untrack_pfn().

These negative effects are caused by two separate bugs, but they
can be dealt in lower priority when PAT is properly initialized.
This patch-set fixes a long-standing PAT initialization issue.

Please see the changelog in patch 3/6 for the details of the
issue.

- Patch 1-2 makes necessary enhancement to PAT for the fix without
  breaking Xen.
- Patch 3 fixes the regression.
- Patch 4 fixes an MTRR issue related with PAT init.
- Patch 5 removes PAT init code from Xen.
- Patch 6 adds PAT init to documentation.

[1]: https://lkml.org/lkml/2016/3/3/828
[2]: https://lkml.org/lkml/2016/3/4/775

I'd appreciate if someone can test this patch-set on Xen to make
sure that there is no change in "x86/PAT: Configuration [0-7] .."
message in dmesg.

---
v2:
 - Divide patch-set into a single change. (Borislav Petkov)
 - Xen's case must be handled properly. (Luis R. Rodriguez)
 - Change changelog and title to describe the issue. (Ingo Molnar)
 - Update an error message. (Robert Elliott, Borislav Petkov)

---
Toshi Kani (6):
 1/6 x86/mm/pat: Change PAT to support non-default PAT MSR
 2/6 x86/mm/pat: Add pat_disable() interface
 3/6 x86/mtrr: Fix Xorg crashes in Qemu sessions
 4/6 x86/mtrr: Fix PAT init handling when MTRR MSR is disabled
 5/6 x86/xen,pat: Remove PAT table init code from Xen
 6/6 x86/pat: Document PAT initializations

---
 Documentation/x86/pat.txt          |  32 ++++++++++++
 arch/x86/include/asm/mtrr.h        |   6 ++-
 arch/x86/include/asm/pat.h         |   2 +-
 arch/x86/kernel/cpu/mtrr/generic.c |  24 +++++----
 arch/x86/kernel/cpu/mtrr/main.c    |  13 ++++-
 arch/x86/kernel/cpu/mtrr/mtrr.h    |   1 +
 arch/x86/mm/pat.c                  | 103 +++++++++++++++++++++++++++++--------
 arch/x86/xen/enlighten.c           |   9 ----
 8 files changed, 146 insertions(+), 44 deletions(-)