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

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Date:	Tue, 29 Mar 2016 12:34:42 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Toshi Kani <toshi.kani@....com>
Cc:	bp@...e.de, hpa@...or.com, tglx@...utronix.de, mcgrof@...e.com,
	jgross@...e.com, paul.gortmaker@...driver.com,
	konrad.wilk@...cle.com, elliott@....com, x86@...nel.org,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes


* Toshi Kani <toshi.kani@....com> 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]: https://lkml.org/lkml/2016/3/3/828
> [2]: https://lkml.org/lkml/2016/3/4/775

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.

Thanks,

	Ingo