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Re: [Xen-devel] [PATCH v3 0/3] map grant refs at pfn = mfn

On 01/08/14 17:16, Thomas Leonard wrote:
On 1 August 2014 16:13, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
On Fri, 1 Aug 2014, Thomas Leonard wrote:
On 24/07/14 14:30, Stefano Stabellini wrote:
Hi all,
this patch series introduces a second p2m mapping of grant reference on
ARM at guest physical address == machine address of the grant ref.  It
is safe because dom0 is already mapped 1:1. We export
XENFEAT_grant_map_identity to signal the guest that this second p2m
mapping is

One reason for wanting the second p2m mapping is to avoid tracking mfn
to pfn mappings in the guest kernel. Since the same mfn can be granted
multiple times to the backend, finding the right pfn corresponding to a
given mfn can be difficult and expensive. Providing a second mapping at
a known address allow the kernel to access the page without knowing the

Is there a version of these patches for Xen 4.4 that I can test? The
restriction on duplicate pages is causing trouble for networking on Mirage too

The backport is non-trivial because
552710b388630dfa461932940a998e120c42277d is missing from 4.4,
nonetheless it wasn't too hard to port:


Thanks. I merged it with the stable-4.4 branch (as that has some
useful fixes too), but it crashed for me when I started my Mirage

You have to drop the BUG_ON line 729.


Julien Grall

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