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Message-ID: <25b7aa40-fad0-4886-90b2-c5d68d75d28b@lucifer.local> Date: Tue, 2 May 2023 16:19:10 +0100 From: Lorenzo Stoakes <lstoakes@...il.com> To: David Hildenbrand <david@...hat.com> Cc: Matthew Rosato <mjrosato@...ux.ibm.com>, Jason Gunthorpe <jgg@...dia.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Jens Axboe <axboe@...nel.dk>, Matthew Wilcox <willy@...radead.org>, Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>, Leon Romanovsky <leon@...nel.org>, Christian Benvenuti <benve@...co.com>, Nelson Escobar <neescoba@...co.com>, Bernard Metzler <bmt@...ich.ibm.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, Bjorn Topel <bjorn@...nel.org>, Magnus Karlsson <magnus.karlsson@...el.com>, Maciej Fijalkowski <maciej.fijalkowski@...el.com>, Jonathan Lemon <jonathan.lemon@...il.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Christian Brauner <brauner@...nel.org>, Richard Cochran <richardcochran@...il.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>, John Hubbard <jhubbard@...dia.com>, Jan Kara <jack@...e.cz>, "Kirill A . Shutemov" <kirill@...temov.name>, Pavel Begunkov <asml.silence@...il.com>, Mika Penttila <mpenttil@...hat.com>, Dave Chinner <david@...morbit.com>, Theodore Ts'o <tytso@....edu>, Peter Xu <peterx@...hat.com> Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings On Tue, May 02, 2023 at 05:09:06PM +0200, David Hildenbrand wrote: > On 02.05.23 15:56, Matthew Rosato wrote: > > On 5/2/23 9:50 AM, Jason Gunthorpe wrote: > > > On Tue, May 02, 2023 at 03:47:43PM +0200, David Hildenbrand wrote: > > > > > Eventually we want to implement a mechanism where we can dynamically pin in response to RPCIT. > > > > > > > > Okay, so IIRC we'll fail starting the domain early, that's good. And if we > > > > pin all guest memory (instead of small pieces dynamically), there is little > > > > existing use for file-backed RAM in such zPCI configurations (because memory > > > > cannot be reclaimed either way if it's all pinned), so likely there are no > > > > real existing users. > > > > > > Right, this is VFIO, the physical HW can't tolerate not having pinned > > > memory, so something somewhere is always pinning it. > > > > I might have mis-explained above. > > > > With iommufd nesting, we will pin everything upfront as a starting point. > > > > The current usage of vfio type1 iommu for s390 does not pin the entirety of guest memory upfront, it happens as guest RPCITs occur / type1 mappings are made. > > ... so, after the domain started successfully on the libvirt/QEMU side ? :/ > > It would be great to confirm that. There might be a BUG in patch #2 (see my > reply to patch #2) that might not allow you to reproduce it right now. > Yes apologies - thank you VERY much for doing this Matthew, but apologies, I made rather a clanger in patch 2 which would mean fast patch degrading to slow path would pass even for file-backed. Will respin a v7 + cc you on that, if you could be so kind as to test that? > -- > Thanks, > > David / dhildenb >
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