Hello Paul,
On 13/06/16 13:12, Paul Durrant wrote:
-----Original Message-----
From: Xen-devel [mailto:[email protected]] On Behalf Of
Julien Grall
Sent: 13 June 2016 11:51
To: [email protected]; David Vrabel; [email protected];
[email protected]; [email protected]
Cc: [email protected]; Andrew Cooper; [email protected];
[email protected]; Julien Grall; [email protected]
Subject: [Xen-devel] [PATCH] xen: grant-table: Check truncation when giving
access to a frame
The version 1 of the grant-table protocol only supports frame encoded on
32-bit.
When the platform is supporting 48-bit physical address, the frame will
be encoded on 36-bit which will lead a truncation and give access to
the wrong frame.
On ARM Xen will always allow the guest to use all the physical address,
although today the RAM is always located under 40-bits (see
xen/include/public/arch-arm.h).
Add a truncation check in gnttab_update_entry_v1 to prevent the guest to
give access to the wrong frame.
Signed-off-by: Julien Grall <[email protected]>
---
This is limiting us to a 44-bit address space whilst ARM can support
up to 48-bit today. This number of bit will increase to 52-bit in
upcoming processors [1].
It might be good to start thinking to extend the version 1 of the
protocol to use 64-bit frame number.
...or simply use version 2 of the protocol.
On another mail [1], you said that "[v2] didn't scale it became
bottle-necked on dom0's grant table size,...".
So it looks like to me that version 2 is the wrong way to go.
The performance should stay the same whether the platform support
40-bit, 44-bit, 48-bit, 52-bit address space.
Regards,
--
Julien Grall
