WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [PATCH] Paging and memory sharing for HVM guests

To: "Grzegorz Milos" <gm281@xxxxxxxxx>, "Patrick Colp" <pjcolp@xxxxxxxxx>, "Andrew Peace" <Andrew.Peace@xxxxxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Paging and memory sharing for HVM guests
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 04 Jan 2010 16:30:09 +0000
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Mon, 04 Jan 2010 08:30:03 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxxx
In-reply-to: <C767BA8C.5659%keir.fraser@xxxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <4B4205B90200007800028173@xxxxxxxxxxxxxxxxxx> <C767BA8C.5659%keir.fraser@xxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 04.01.10 16:32 >>>
>On 04/01/2010 14:14, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>
>> Isn't this undermining the purpose of privcmd_enforce_singleshot_mapping()?
>> You don't check that the eventual single page re-mapping attempt is
>> really due to an earlier -ENOENT failure, and hence the whole single
>> shot mapping checks are now pointless (though other than possibly to
>> enforce some minimal security I don't really know what its purpose
>> is/was - Keir?).
>
>It was just to avoid the BUG_ON(!pte_none(*pte)) in
>direct_remap_area_pte_fn(). We trust privcmd users enough we could just get
>rid of privcmd_enforce_singleshot_mapping(). We could instead forcibly clear
>ptes before calling direct_remap_area(); or just do nothing.

I'm of the opinion that even privileged users shouldn't be able to oops
the kernel, and hence hitting the BUG_ON() you're mentioning should
be avoided. Clearing the old mappings seems like a reasonable thing
to do.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel