linux-kernel - Re: [PATCH v2 1/1] fs/splice: add missing callback for inaccessible pages

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Date:   Tue, 5 May 2020 16:00:10 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Ulrich Weigand <uweigand@...ibm.com>
Cc:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, viro@...iv.linux.org.uk,
        david@...hat.com, akpm@...ux-foundation.org, aarcange@...hat.com,
        linux-mm@...ck.org, frankja@...ux.ibm.com, sfr@...b.auug.org.au,
        jhubbard@...dia.com, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, jack@...e.cz, kirill@...temov.name,
        peterz@...radead.org, sean.j.christopherson@...el.com,
        Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH v2 1/1] fs/splice: add missing callback for inaccessible
 pages



On 05.05.20 14:34, Dave Hansen wrote:[...]
>> I'm not sure what exactly the requirements for your use case are; if those
>> are significantly differently, maybe we can work together to find an
>> approach that works for both?
> 
> I'm actually trying to figure out what to do with AMD's SEV.  The
> current state isn't great and, for instance, allows userspace to read
> guest ciphertext.  But, the pages come and go out of the encrypted state
> at the behest of the guest, and the kernel needs *some* mapping for the
> pages to do things like instruction emulation.
> 
> I started looking at s390 because someone said there was a similar
> problem there and suggested the hooks might work.  I couldn't figure out
> how they worked comprehensively on s390, and that's how we got here.

We are certainly not married to our approach. I would happily extend/change
this to anything that works for your case and the s390 case. So can you outline
your requirements a  bit more?