Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes

From: Ingo Molnar
Date: Tue Mar 29 2016 - 06:34:56 EST

* Toshi Kani <toshi.kani@xxxxxxx> wrote:

> 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]:
> [2]:

The changelogs are much improved, I've applied these patches to tip:x86/mm,
thanks Toshi!

> 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.

So I don't have a Xen setup, but hopefully such testing will happen once these
changes show up in linux-next, tomorrow or so.