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Re: [Xen-devel] Xen 3.2.1-rc1: Assertion '!(*ar & ( 3<<13))' failed at t

To: "Christopher S. Aker" <caker@xxxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen 3.2.1-rc1: Assertion '!(*ar & ( 3<<13))' failed at traps.c:1305
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 08 Apr 2008 07:46:59 +0100
Cc: jeremy@xxxxxxxx
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Thread-topic: [Xen-devel] Xen 3.2.1-rc1: Assertion '!(*ar & ( 3<<13))' failed at traps.c:1305
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On 7/4/08 20:43, "Christopher S. Aker" <caker@xxxxxxxxxxxx> wrote:

> We've set up a few xen-thrash environments, which are a mix of a nodes
> being created and destroyed, created and shutdown, long running
> swap-thrashing nodes, long-running crashme nodes, etc.  About 50 domains
> in total.  We've managed to hit a crash!
> Xen:
> http://www.theshore.net/~caker/xen/BUGfatal_page_fault/
> domU:
> http://www.theshore.net/~caker/xen/kernels/
> On this particular host, we're running all pv_ops guest kernels.  Trace
> as follows:
> (XEN) traps.c:2540: GPF (9898): ffff828c8014c387 -> ffff828c801be667
> (XEN) traps.c:2540: GPF (c708): ffff828c8014c387 -> ffff828c801be667
> (XEN) Assertion '!(*ar & ( 3<<13))' failed at traps.c:1305

Weird error condition (which may well mean the domU is doomed) has triggered
an unexpected path in Xen. I'll give the code concerned an audit and at the
very least I should be able to fix the host crash (hopefully, unless weird
corruption really must have happened).

The GPFs are interesting -- those are very big and random looking segment
selector values (9898 c708), rather like someone is trying load random
numbers into segment registers. It reminds me of the first crash you posted
about, which was a random number turning up in a page directory entry. I
wonder if there is a common cause.

 -- Keir

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