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[Xen-devel] Re: RFC: Using grant table to give iomem permission

To: "Lamia M. Youseff" <lyouseff@xxxxxxxxxxx>
Subject: [Xen-devel] Re: RFC: Using grant table to give iomem permission
From: Kieran Mansley <kmansley@xxxxxxxxxxxxxx>
Date: Mon, 21 May 2007 11:36:05 +0100
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On Fri, 2007-05-18 at 12:11 -0700, Lamia M. Youseff wrote:
> > When the hypervisor tries to do this grant in xen/common/grant_table.c
> > it (i) notices that it is an iomem_map rather than device_map or
> > host_map; (ii) it is from dom0; and (iii) it is not a RAM page.  It then
> > attempts to call iomem_permit_access().
> Hi Karen, 
> Thanks for the patch, I find it useful... but I am wondering why you
> need to check it is from a dom0 ... I maybe not getting the reason,
> but iomem_map should be available for page sharing among all domains,
> shouldn't it ?

There's no absolute requirement for that check to be there, but it is
something that came out of discussion with Keir.  It seems sensible to
me to only allow dom0 to programatically give access to iomem, as
typically this is used to access physical hardware.  I think most guest
domains wouldn't have any iomem regions available to them that they
would want to share.  If they did, access to this could be currently
configured using the Xen tools (I think - not actually tried this).


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