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Re: [Xen-devel] Xen dev help required

To: Brad Plant <bplant@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen dev help required
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Wed, 18 Feb 2009 17:42:49 -0800
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Brad Plant wrote:
Hi list,

I was hoping some people "in the know" about how the hypervisor works etc could 
take a look at the thread below and hopefully offer some advice.

http://forums.grsecurity.net/viewtopic.php?f=1&t=2063&p=8759#p8745

The PaX developers are trying to get their patch to work on a 2.6.28 
paravirt_ops kernel. They already have PaX working with a 2.6.27 paravirt_ops 
kernel, but a recent change to the PaX patch, specifically to map up to 4GB 
initially in the identity map is causing the kernel to panic when booted under 
xen.

Any help on the matter would be greatly appreciated by all.

Looks like what they're trying to do is pretty redundant; Xen is pretty good at protecting the kernel's pagetables for it. From just looking at that piece of thread, I'm guessing they're creating writeable aliases of the pagetable pages, which Xen won't allow.

Yeah, this one:
|(XEN) mm.c:794:d35 Attempt to create linear p.t. with write perms

|    J

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