Re: [PATCH v2 0/6] gnttab: add per-domain controls

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.09.2021 09:30, Julien Grall wrote:
> On Fri, 24 Sep 2021, 11:21 Jan Beulich, <jbeulich@xxxxxxxx> wrote:
>> On 24.09.2021 04:30, Julien Grall wrote:
>>> On Thu, 23 Sep 2021, 16:20 Roger Pau Monné, <roger.pau@xxxxxxxxxx>
>> wrote:
>>>> On Thu, Sep 23, 2021 at 01:47:37PM +0500, Julien Grall wrote:
>>>>> On 22/09/2021 14:39, Roger Pau Monné wrote:
>>>>>> On Wed, Sep 22, 2021 at 01:57:02PM +0500, Julien Grall wrote:
>>>>>>> On 22/09/2021 13:21, Roger Pau Monne wrote:
>>>>>> But it's also arguable that a guest not having a grant table should
>>>>>> also likely prevent foreign mapping attempts. Plus such foreign
>>>>>> mapping won't work from stubdomains.
>>>>>
>>>>> There is another option: extend the acquire hypercall to allow
>> xenstored
>>>>> domain to map the xenstore interface. This would require more work, but
>>>> at
>>>>> least it would avoid the interesting dependency on the grant table.
>>>>
>>>> Xen isn't aware of the shared xenstore ring page currently, so that
>>>> would mean introducing more knowledge to the hypervisor that what's
>>>> strictly required IMO, as Xen has no business in knowing such details.
>>>>
>>>
>>> Well Xen already knows the page for HVM/PVH because the guest retrieve it
>>> through an HMV param.
>>
>> To be honest using this in such a way would feel like an abuse / layering
>> violation to me.
>>
> 
> I can see how it can be seen like this. Do you have a better suggestion to
> be able to map mapping without the foreign mapping interface and the grant
> table?

Well, as was mentioned, PV would need covering anyway. And I think just
like with grants the guest should consent with such foreign mappings
outside of the "can map everything anyway" category. Hence I think if
such a capability is indeed needed/wanted, it ought to be the guest to
announce this page to Xen.

Jan