On Thu, 2010-02-25 at 10:18 +0100, Bastian Blank wrote:
On Thu, Feb 25, 2010 at 07:33:26AM +, Ian Campbell wrote:
Is it acceptable to backport
http://git.kernel.org/?p=linux/kernel/git/tip/linux-2.6-tip.git;a=commitdiff;h=a73a040e3b18521f83e726abacc2f3992a148388
into the sid kernel?
Will it show up in Linus tree any time soon?
Hopefully in the 2.6.33 merge window but I will check with x86
maintainers.
The followup Xen patch is
http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=commitdiff;h=9be6abceadd654543648b799ae430f30e09959ac
and disables HIGHPTE when running under Xen. It prevents crashes under
load due to HIGHPTE races which cannot be otherwise (easily) avoided
under Xen.
The commit message does not describe why, and it is not obvious to me.
It's a race between pinning a page and kmap/kunmap. There's a path in
the pagefault code where the kernel breaks its own locking rules by
kmapping a high pte page without holding the pagetable lock which breaks
Xen's ability to track the pinned/unpinned state of the page. (I'm going
to ask Jeremy to update the commit to include this paragraph of
explanation).
Jeremy gave some explanation in:
http://lists.xensource.com/archives/html/xen-devel/2010-01/msg00921.html
(which I've blatantly stolen above)
The thread which led to the patch is [Xen-devel] dom0 pvops crash and
[Xen-devel] Xen pvops kernel CONFIG_HIGHPTE race/crash involving Pasi
Kärkkäinen. It's quite long but the final conclusion starts at:
http://lists.xensource.com/archives/html/xen-devel/2010-02/msg00403.html
That thread starts at:
http://lists.xensource.com/archives/html/xen-devel/2010-01/msg00902.html
and there is an older version of the same issue at:
http://lists.xensource.com/archives/html/xen-devel/2009-06/msg00519.html
I'm not sure, but I think this should be possible to do via stable after
both patches landed where they belong.
OK will go that route assuming I get confirmation that the patch is
destined for 2.3.32. If not then would a backport be appropriate?
Ian.
--
Ian Campbell
Current Noise: Autopsy - Pagan Saviour (Live '90)
Q: Why haven't you graduated yet?
A: Well, Dad, I could have finished years ago, but I wanted
my dissertation to rhyme.
--
To UNSUBSCRIBE, email to debian-kernel-requ...@lists.debian.org
with a subject of unsubscribe. Trouble? Contact listmas...@lists.debian.org
Archive:
http://lists.debian.org/1267109053.11737.10729.ca...@zakaz.uk.xensource.com
