Re: [Xen-devel] [PATCH 2/2] memory: don't hand MFN info to translated guests

[Tamas K Lengyel <tamas.k.lengyel@xxxxxxxxx>]

On Tue, Apr 4, 2017 at 1:04 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 04/04/17 14:14, Jan Beulich wrote:
>> We shouldn't hand MFN info back from increase-reservation for
>> translated domains, just like we don't for populate-physmap and
>> memory-exchange. For full symmetry also check for a NULL guest handle
>> in populate_physmap() (but note this makes no sense in
>> memory_exchange(), as there the array is also an input).
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Unfortunately I just had time to do testing with this change and I
have to report that introduces a critical regression for my tools.
With this change in-place performing increase_reservation on a target
domain no longer reports the guest frame number for external tools,
thus completely breaking advanced use-cases that require this
information to be able to do altp2m gfn remapping. This is a critical
step in being able to introduce shadow-pages that are used to hide
breakpoints and other memory modifications from the guest.

If at all possible, I would like to request this change not to be part
of the 4.9 release.

Thanks,
Tamas

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