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Re: [PATCH v1 03/12] s390x/tcg: convert real to absolute address for RRB

From: David Hildenbrand
Subject: Re: [PATCH v1 03/12] s390x/tcg: convert real to absolute address for RRBE, SSKE and ISKE
Date: Fri, 6 Aug 2021 13:32:57 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

On 06.08.21 13:25, Cornelia Huck wrote:
On Fri, Aug 06 2021, David Hildenbrand <david@redhat.com> wrote:

On 06.08.21 09:11, Thomas Huth wrote:
On 06/08/2021 08.52, David Hildenbrand wrote:

According to the PoP:

"When the enhanced-DAT facility 1 is not installed, or
     when the facility is installed but the multiple-block
     control is zero, general register R 2 contains a real
     address. When the enhanced-DAT facility 1 is
     installed and the multiple-block control is one, gen-
     eral register R 2 contains an absolute address."

Don't we have to take that into consideration here, too?

We don't support EDAT1 a.k.a. huge pages yet. If we ever do, we have to
further extend this code.

Ok, then maybe add a comment or assert() to make sure that we don't forget?

Well, we'll need modifications and extensions all over the place to
support EDAT1, so I'm not sure this will really help ... we'll have to
carefully scan the PoP either way.

Something like
/* always real address, as long as we don't implement EDAT1 */
would still be useful, I think.

I am not a friend of describing what to be done with additional CPU features. We have the PoP for that: just imagine you read an old version of the PoP, the code as is would make perfect sense even without ever knowing what EDAT1 is -- and you can verify that the code is correct.

For now I added to the patch description:

In the future, when adding EDAT1 support, we'll have to pay attention to
SSKE handling, as we'll be dealing with absolute addresses when the
multiple-block control is one.


David / dhildenb

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