Re: [RFC/PATCH v3 04/16] s390/mm: add gmap PMD invalidation notification

[David Hildenbrand <david@redhat.com>]

>>>> That's interesting, because the SIE can now suddenly work on these
>>>> PGSTEs, e.g. not leading to intercepts on certain events (like setting
>>>> storage keys).
>>>>
>>>> How is that intended to be handled? I assume we would somehow have to
>>>> forbid the SIE from making use of the PGSTE. But that involves clearing
>>>> certain interception controls, which might be problematic.
>>>
>>> Well, cmma is disabled and storage keys should only be a problem, when
>>> the pte is invalid without the pgste lock, which should never be the
>>> case for split pmds.
>>>
>>
>> Are you sure? Because the SIE would suddenly stark working on guest
>> storage keys stored in the PGSTE if I am not mistaking? So I would
>> assume that there would have to be some kind of a sync.
>>
>> But I don't have any documentation at hand, so i can't tell :)
>>
> 
> The pgste lock is that sync and as the gmap is the only way to get to
> the pte, we don't have any ptes invalid without the lock. Also
> set_guest_storage_keys will find a (userspace) pmd and do a hardware
> sske, like it is supposed to.

What happens according to the documentation in the following cases:

The HW has the storage-key facility enabled and a SKEY operation (ISKE,
RRBE, SSKE) hits a huge page:

a) Generates an intercept
b) Uses the real machine storage key (as there are no pgste)

-- 

Thanks,

David / dhildenb