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Subject[PATCH v3 0/7] Enhance PAT init to fix Xorg crashes
Date
A Xorg failure on qemu32 was reported as a regression [1] caused by
'commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")'.
This patch-set fixes the regression.

Negative effects of this regression were two failures [2] in Xorg on
QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were triggered
by the fact that its virtual CPU does not support MTRR.
#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
addressed in separate patches. This patch-set addresses the root cause,
a long-standing PAT initialization issue.

Please see the changelog in patch 4/7 for the details of the issue.

- Patch 1-2 make necessary enhancement to PAT for the fix without
breaking Xen.
- Patch 3 is cleanup.
- Patch 4 fixes the regression.
- Patch 5 fixes an MTRR issue related with PAT init.
- Patch 6 removes PAT init code from Xen.
- Patch 7 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 verify that
there is no change in "x86/PAT: Configuration [0-7] .." message in dmesg.

---
v3:
- Change a new func name to init_cache_modes(). (Borislav Petkov)
- Add check with __pat_enabled, and use WARN_ONCE() for a bug check
in pat_disable(). (Borislav Petkov)
- Update changelog, comments, and doc per review. (Borislav Petkov)

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 (7):
1/7 x86/mm/pat: Add support of non-default PAT MSR setting
2/7 x86/mm/pat: Add pat_disable() interface
3/7 x86/mm/pat: Replace cpu_has_pat with boot_cpu_has
4/7 x86/mtrr: Fix Xorg crashes in Qemu sessions
5/7 x86/mtrr: Fix PAT init handling when MTRR is disabled
6/7 x86/xen,pat: Remove PAT table init code from Xen
7/7 x86/pat: Document PAT initialization

---
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 | 90 ++++++++++++++++++++++++++++----------
arch/x86/xen/enlighten.c | 9 ----
8 files changed, 132 insertions(+), 45 deletions(-)

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