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Re: [PATCH 03/10] xen/arm: introduce PGC_reserved

Hi Jan,

On 20/05/2021 10:27, Jan Beulich wrote:
On 20.05.2021 10:59, Julien Grall wrote:
On 20/05/2021 09:40, Penny Zheng wrote:
Oh, Second thought on this.
And I think you are referring to balloon in/out here, hmm, also, like

Yes I am referring to balloon in/out.

I replied there:
"For issues on ballooning out or in, it is not supported here.

So long you are not using the solution in prod then you are fine (see
below)... But then we should make clear this feature is a tech preview.

Domain on Static Allocation and 1:1 direct-map are all based on
dom0-less right now, so no PV, grant table, event channel, etc, considered.

Right now, it only supports device got passthrough into the guest."

So we are not creating the hypervisor node in the DT for dom0less domU.
However, the hypercalls are still accessible by a domU if it really
wants to use them.

Therefore, a guest can easily mess up with your static configuration and

IMHO, this is a must to solve before "static memory" can be used in

I'm having trouble seeing why it can't be addressed right away:

It can be solved right away. Dom0less domUs don't officially know they are running on Xen (they could bruteforce it though), so I think it would be fine to merge without it for a tech preview.

guests can balloon in only after they've ballooned out some pages,
and such balloon-in requests would be satisfied from the same static
memory that is associated by the guest anyway.

This would require some bookeeping to know the page was used previously. But nothing very challenging though.


Julien Grall



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