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

[Jan Beulich <jbeulich@xxxxxxxx>]

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

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

Jan