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Date:   Tue, 2 May 2023 15:28:40 +0200
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To:     Jason Gunthorpe <jgg@nvidia.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>
Cc:     Lorenzo Stoakes <lstoakes@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>,
        Matthew Wilcox <willy@infradead.org>,
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        Leon Romanovsky <leon@kernel.org>,
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        Bernard Metzler <bmt@zurich.ibm.com>,
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        Arnaldo Carvalho de Melo <acme@kernel.org>,
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        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
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        Adrian Hunter <adrian.hunter@intel.com>,
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        Magnus Karlsson <magnus.karlsson@intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
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        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Christian Brauner <brauner@kernel.org>,
        Richard Cochran <richardcochran@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
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        Oleg Nesterov <oleg@redhat.com>,
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        Theodore Ts'o <tytso@mit.edu>, Peter Xu <peterx@redhat.com>,
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 <a6bb0334-9aba-9fd8-6a9a-9d4a931b6da2@linux.ibm.com>
 <ZFEL20GQdomXGxko@nvidia.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to
 file-backed mappings
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On 02.05.23 15:10, Jason Gunthorpe wrote:
> On Tue, May 02, 2023 at 03:04:27PM +0200, Christian Borntraeger wrote:
> \> > We can reintroduce a flag to permit exceptions if this is really broken, are you
>>> able to test? I don't have an s390 sat around :)
>>
>> Matt (Rosato on cc) probably can. In the end, it would mean having
>>    <memoryBacking>
>>      <source type="file"/>
>>    </memoryBacking>
> 
> This s390 code is the least of the problems, after this series VFIO
> won't startup at all with this configuration.

Good question if the domain would fail to start. I recall that IOMMUs 
for zPCI are special on s390x. [1]

Well, zPCI is special. I cannot immediately tell when we would trigger 
long-term pinning.

[1] https://www.mail-archive.com/qemu-devel@nongnu.org/msg875728.html

-- 
Thanks,

David / dhildenb