linux-kernel - Re: patch x86-xen-disable-highmem-pte-allocation-even-when-config_highpte-y.patch added to 2.6.33-stable tree

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Date:	Fri, 12 Mar 2010 14:17:33 +0000
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Stefan Lippers-Hollmann <s.L-H@....de>
CC:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"jeremy@...p.org" <jeremy@...p.org>,
	"mingo@...e.hu" <mingo@...e.hu>, "pasik@....fi" <pasik@....fi>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: patch
 x86-xen-disable-highmem-pte-allocation-even-when-config_highpte-y.patch
 added to 2.6.33-stable tree

On Fri, 2010-03-12 at 14:08 +0000, Stefan Lippers-Hollmann wrote:
> Hi
> 
> On Friday 12 March 2010, gregkh@...e.de wrote:
> > This is a note to let you know that we have just queued up the patch titled
> > 
> >     Subject: x86, xen: Disable highmem PTE allocation even when CONFIG_HIGHPTE=y
> > 
> > to the 2.6.33-stable tree.  Its filename is
> > 
> >     x86-xen-disable-highmem-pte-allocation-even-when-config_highpte-y.patch
> > 
> > A git repo of this tree can be found at 
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > 
> > From 817a824b75b1475f1b067c8cee318c7b4d66fcde Mon Sep 17 00:00:00 2001
> > From: Ian Campbell <ian.campbell@...rix.com>
> > Date: Fri, 26 Feb 2010 17:16:00 +0000
> > Subject: x86, xen: Disable highmem PTE allocation even when CONFIG_HIGHPTE=y
> > MIME-Version: 1.0
> > Content-Type: text/plain; charset=UTF-8
> > Content-Transfer-Encoding: 8bit
> > 
> > From: Ian Campbell <ian.campbell@...rix.com>
> > 
> > commit 817a824b75b1475f1b067c8cee318c7b4d66fcde upstream.
> > 
> > There's a path in the pagefault code where the kernel deliberately
> > breaks its own locking rules by kmapping a high pte page without
> > holding the pagetable lock (in at least page_check_address). This
> > breaks Xen's ability to track the pinned/unpinned state of the
> > page. There does not appear to be a viable workaround for this
> > behaviour so simply disable HIGHPTE for all Xen guests.
> 
> This patch breaks compilation of the current 2.6.33 -stable queue and might
> also affect queue-2.6.32 (untested):
> 
>   CC      arch/x86/xen/enlighten.o
> arch/x86/xen/enlighten.c: In function ‘xen_start_kernel’:
> arch/x86/xen/enlighten.c:1102: error: ‘__userpte_alloc_gfp’ undeclared (first use in this function)
> arch/x86/xen/enlighten.c:1102: error: (Each undeclared identifier is reported only once
> arch/x86/xen/enlighten.c:1102: error: for each function it appears in.)
> make[2]: *** [arch/x86/xen/enlighten.o] Error 1
> make[1]: *** [arch/x86/xen] Error 2
> 
> as it seems to depend (tested) on:
> 
> commit 14315592009c17035cac81f4954d5a1f4d71e489
> Author: Ian Campbell <ian.campbell@...rix.com>
> Date:   Wed Feb 17 10:38:10 2010 +0000
> 
>     x86, mm: Allow highmem user page tables to be disabled at boot time

Thanks Stefan, this is indeed the correct fix. I pointed Greg to this
patch in private mail this morning.

Ian.



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