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Re: [Xen-devel] [PATCH] xen: grant-table: Simplify get_page_frame

Hi Jan,

On 09/15/2017 01:15 PM, Jan Beulich wrote:
On 14.09.17 at 18:49, <julien.grall@xxxxxxx> wrote:
get_page_from_gfn will be able to get reference on foreign page and as
per my understanding will allow to grant page on foreign memory.

This was not allowed with a simple get_page(...) on the ARM
implementation (no sharing nor paging supprot) but is allowed on the x86
implementation due to get_page_from_gfn.

On x86, foreign pages are currently only allowed for PVH dom0, so I
think it is not a big deal for now.

On Arm, foreign pages can be present on any domain. So this patch would
permit grant on foreing pages.

So I would like to check whether it would be valid to grant a mapping on
foreign pages?

No, I don't think grants should be permitted for other domains'

Which seems to match the PV behavior. I will update the patch to forbid foreign pages and use #ifdef.


Julien Grall

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