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Re: [Xen-devel] [PATCH] xen/altp2m: set access_required properly for all altp2ms

On 06/12/2018 03:35 PM, Razvan Cojocaru wrote:
>>> @@ -210,7 +211,7 @@ static int p2m_init_altp2m(struct domain *d)
>>>              return -ENOMEM;
>>>          }
>>>          p2m->p2m_class = p2m_alternate;
>>> -        p2m->access_required = 1;
>>> +        p2m->access_required = hostp2m->access_required;
>> There must have been a reason to have it start out as 1. You
>> mention the fact in the description, but not why it is okay (or
>> even necessary) to change it.
> If there was one, I can't see what it was. It in any case make altp2ms
> behave differently than the hostp2m. The mem_access system has been
> designed so that the user can say "this domain should now no longer be
> able to continue if there are EPT violatios and there's no vm_event
> subscriber attached".
> Our application, for one, explicitly _disables_ access_required - so
> that it is able to detach from the domain and reattach later. Hence the
> surprise when an altp2m-enabled domain crashed when the introspection
> agent detached.
> Basically, the altp2m behaviour can't be controlled at all here. Maybe
> Tamas remembers / knows more about why access_required ended up being 1
> always, but it was probably just the quickest way to write the original
> patch.

CCd Tamas.

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