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

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On 14.02.2018 11:42, David Hildenbrand wrote:
> 
>>>>> 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)
> 

b, this is an implicit RCP bypass (same goes for fc=1 r3 entries). This
might be even independent of the SKF if I'm not mistaken.

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