From mboxrd@z Thu Jan  1 00:00:00 1970
From: Corneliu ZUZU <czuzu@bitdefender.com>
Subject: Re: [PATCH] x86/hvm: Fix use-after-free introduced by
 c/s 428607a
Date: Tue, 2 Feb 2016 14:51:11 +0200
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On 2/2/2016 2:05 PM, Andrew Cooper wrote:
> Xen and PV guests share the virtual address space, in exactly the same 
> way as a native kernel and its userspace. PV guests can map pages at 
> 0. Therefore, if Xen were to accidentally follow a NULL pointer, it 
> may not result in a pagefault. (Hardware mechanisms such as SMEP and 
> SMAP are added protection against this, but don't work on older hardware)
> ~Andrew 

Thank you, I finally got it.
(I also read 
http://wiki.xenproject.org/wiki/X86_Paravirtualised_Memory_Management , 
cleared things up)

Corneliu.