Message-ID: <1459261167.6393.668.camel@hpe.com>
Subject: Re: [PATCH v3 0/7] Enhance PAT init to fix Xorg crashes
From: Toshi Kani <toshi.kani@hpe.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: bp@suse.de, hpa@zytor.com, tglx@linutronix.de, mcgrof@suse.com,
        jgross@suse.com, paul.gortmaker@windriver.com, konrad.wilk@oracle.com,
        elliott@hpe.com, x86@kernel.org, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
Date: Tue, 29 Mar 2016 08:19:27 -0600
In-Reply-To: <20160329103442.GA12645@gmail.com>
References: <1458769323-24491-1-git-send-email-toshi.kani@hpe.com>
	 <20160329103442.GA12645@gmail.com>
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On Tue, 2016-03-29 at 12:34 +0200, Ingo Molnar wrote:
> * Toshi Kani <toshi.kani@hpe.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!

Great! Thanks for all valuable comments!

> > 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.

I will address if any issue is found in testing.

-Toshi