Xen devel - Jul 2007 - Grant Table problem mapping dom0 mem to domU

I''ve been looking through some back-end drivers and I notice that
grant tables are used to map domU memory into the privileged domain,
is the opposite possible? Can I map dom0 memory into a domU?

I''ve written code grants foreign access to a page from dom0 (take the
grant ref_id) then on domU I try to map it (basically the same way ex
blkback does it, or just any other driver for that matter) and all I
get from HYPERVISOR_grant_table_op() is a -1 return value, op.status
is empty=0.

I''ll send more information on the specific error, if I at least know
that this can be done and I''m just not falling of a cliff. Also, if it
is possible, can you point me to some example code?

thanks,
C. René

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Hi Carlos,

The problem you are facing is that the grant_operation_permitted()  
test (in the GNTTABOP_map_grant_ref case of the do_grant_table_op  
function in xen/common/grant_table.c) is failing. At present, only  
domains with iomem permissions can map grant references: typically,  
the only such domain is dom0. This is due to a TLB flush issue which  
was addressed in a recent patchset from Kieran Mansley. You can  
either try giving some dummy iomem privileges to your domU, or change  
the definition of grant_operation_permitted(d) to 1, so that it  
always succeeds.

Regards,

Derek Murray.

On 25 Jul 2007, at 16:41, Carlos Perez wrote:
> I''ve been looking through some back-end drivers and I notice that
> grant tables are used to map domU memory into the privileged domain,
> is the opposite possible? Can I map dom0 memory into a domU?
>
> I''ve written code grants foreign access to a page from dom0 (take
the
> grant ref_id) then on domU I try to map it (basically the same way ex
> blkback does it, or just any other driver for that matter) and all I
> get from HYPERVISOR_grant_table_op() is a -1 return value, op.status
> is empty=0.
>
> I''ll send more information on the specific error, if I at least
know
> that this can be done and I''m just not falling of a cliff. Also,
if it
> is possible, can you point me to some example code?
>
> thanks,
> C. René
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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On Wed, 2007-07-25 at 16:59 +0100, Derek Murray wrote:
> This is due to a TLB flush issue which  
> was addressed in a recent patchset from Kieran Mansley. 
To which I''ve just posted an updated version due to a bug I''d
missed.
The patch as it stands doesn''t however change the definition of
grant_operation_permitted(), so if using that patch you''d still need to
make that change manually to get any benefit (other than correctness)
from it.

Kieran


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Thanks guys, that totally solved the problem.

On 7/25/07, Derek Murray <Derek.Murray@cl.cam.ac.uk>
wrote:
> Hi Carlos,
>
> The problem you are facing is that the grant_operation_permitted()
> test (in the GNTTABOP_map_grant_ref case of the do_grant_table_op
> function in xen/common/grant_table.c) is failing. At present, only
> domains with iomem permissions can map grant references: typically,
> the only such domain is dom0. This is due to a TLB flush issue which
> was addressed in a recent patchset from Kieran Mansley. You can
> either try giving some dummy iomem privileges to your domU, or change
> the definition of grant_operation_permitted(d) to 1, so that it
> always succeeds.
>
> Regards,
>
> Derek Murray.
>
> On 25 Jul 2007, at 16:41, Carlos Perez wrote:
>
> > I''ve been looking through some back-end drivers and I notice
that
> > grant tables are used to map domU memory into the privileged domain,
> > is the opposite possible? Can I map dom0 memory into a domU?
> >
> > I''ve written code grants foreign access to a page from dom0
(take the
> > grant ref_id) then on domU I try to map it (basically the same way ex
> > blkback does it, or just any other driver for that matter) and all I
> > get from HYPERVISOR_grant_table_op() is a -1 return value, op.status
> > is empty=0.
> >
> > I''ll send more information on the specific error, if I at
least know
> > that this can be done and I''m just not falling of a cliff.
Also, if it
> > is possible, can you point me to some example code?
> >
> > thanks,
> > C. René
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
> h
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