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

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>> So what can happen is (please correct me if I'm wrong)
>>
>> a) PMD is split. SSKE writes storage key with _PAGE_CHANGED, ends up in
>> PGSTE. The real storage key doesn't match the requested storage key.
>> b) Split PMD is replaced, triggers a removal of the split PMD ->
>> gmap_pmd_split_free(pmdp). The requested storage key is partially lost
>> (pgste removed).
>> c) PMD is mapped in again. If the guest reads the storage key now, the
>> value is wrong.
> 
> Yes, we loose GR and GC.
> Is there a case when the VM is running, where this would happen?

It should already happen when migrating storage keys. The fake PGSTE are
not considered in get_guest_storage_key().

For the other parts, the original user space PMD would have to be
changed. A simply mprotect() should achieve that. Or dirty tracking. But
not sure how that applies to huge pages at all.

-- 

Thanks,

David / dhildenb
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