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Date:   Tue, 15 Mar 2022 17:58:42 +0100
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Subject: Re: [PATCH v1 5/7] s390/pgtable: support
 __HAVE_ARCH_PTE_SWP_EXCLUSIVE
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From:   David Hildenbrand <david@redhat.com>
To:     Gerald Schaefer <gerald.schaefer@linux.ibm.com>
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        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
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        Mike Kravetz <mike.kravetz@oracle.com>,
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>> This would mean that it is not OK to have bit 52 not zero for swap PTEs.
>> But if I read the POP correctly, all bits except for the DAT-protection
>> would be ignored for invalid PTEs, so maybe this comment needs some update
>> (for both bits 52 and also 55).
>>
>> Heiko might also have some more insight.
> 
> Indeed, I wonder why we should get a specification exception when the
> PTE is invalid. I'll dig a bit into the PoP.

SA22-7832-12 6-46 ("Translation-Specification Exception") is clearer

"The page-table entry used for the translation is
valid, and bit position 52 does not contain zero."

"The page-table entry used for the translation is
valid, EDAT-1 does not apply, the instruction-exe-
cution-protection facility is not installed, and bit
position 55 does not contain zero. It is model
dependent whether this condition is recognized."

-- 
Thanks,

David / dhildenb