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Date:   Tue, 2 May 2023 09:38:28 -0400
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Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to
 file-backed mappings
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To:     David Hildenbrand <david@redhat.com>,
        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>,
        Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
        Leon Romanovsky <leon@kernel.org>,
        Christian Benvenuti <benve@cisco.com>,
        Nelson Escobar <neescoba@cisco.com>,
        Bernard Metzler <bmt@zurich.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Bjorn Topel <bjorn@kernel.org>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        "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>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        Oleg Nesterov <oleg@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>, Jan Kara <jack@suse.cz>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Mika Penttila <mpenttil@redhat.com>,
        Dave Chinner <david@fromorbit.com>,
        "Theodore Ts'o" <tytso@mit.edu>, Peter Xu <peterx@redhat.com>
References: <cover.1682981880.git.lstoakes@gmail.com>
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 <fbad9e18-f727-9703-33cf-545a2d33af76@linux.ibm.com>
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 <a6bb0334-9aba-9fd8-6a9a-9d4a931b6da2@linux.ibm.com>
 <ZFEL20GQdomXGxko@nvidia.com>
 <c4f790fb-b18a-341a-6965-455163ec06d1@redhat.com>
From:   Matthew Rosato <mjrosato@linux.ibm.com>
In-Reply-To: <c4f790fb-b18a-341a-6965-455163ec06d1@redhat.com>
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On 5/2/23 9:28 AM, David Hildenbrand wrote:
> 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]

Eh, well what you referenced there never merged.  We will eventually do something like this, but via iommufd.  But right now s390 is still using vfio type1 iommu

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

Enabling a zPCI device in a QEMU guest when using zPCI interpretation facilities

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