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Re: [Xen-devel] RE: Biweekly VMX status report. Xen: #20255 & Xen0:#b6ba

To: "Xu, Jiajun" <jiajun.xu@xxxxxxxxx>, "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RE: Biweekly VMX status report. Xen: #20255 & Xen0:#b6ba0...
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 30 Sep 2009 07:57:04 +0100
Cc: "Xin, Xiaohui" <xiaohui.xin@xxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "Han, Weidong" <weidong.han@xxxxxxxxx>, "Li, Xin" <xin.li@xxxxxxxxx>, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
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On 30/09/2009 02:15, "Xu, Jiajun" <jiajun.xu@xxxxxxxxx> wrote:

>> 1. Booting guest with device assigned & EPT enabled cause xen crash
>> http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1518
> 
> For the above bug, it's a regression which does not exist in xen c/s 20187.
> Could anyone help to fix it?
> 
> It's likely that the issue is introduced by the "pod for EPT" patches
> (20191~20197).

It is caused by the addition of an assertion that p2m_is_locked_by_me in
ept_sync_domain(). This was done because that function needs to be
serialised, and we expected that anyone coming through set_p2m_entry() would
have the p2m_lock held.

So, we could 'fix' by giving ept_sync_domain() its own lock, but my
suspicion would be that any paths through the p2m code that are not holding
the p2m_lock probably need to be fixed. Adjusting p2m entries without the
lock held sounds racey to me.

 -- Keir



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