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[2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id d23-20020a1c7317000000b003f325f0e020sm13416157wmb.47.2023.05.02.08.09.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 08:09:08 -0700 (PDT) Message-ID: <1f3231c0-34b2-1e78-0bf0-f32d5b67811d@redhat.com> Date: Tue, 2 May 2023 17:09:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings To: Matthew Rosato , Jason Gunthorpe Cc: Christian Borntraeger , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Jens Axboe , Matthew Wilcox , Dennis Dalessandro , Leon Romanovsky , Christian Benvenuti , Nelson Escobar , Bernard Metzler , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Bjorn Topel , Magnus Karlsson , Maciej Fijalkowski , Jonathan Lemon , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Christian Brauner , Richard Cochran , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , linux-fsdevel@vger.kernel.org, linux-perf-users@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org, Oleg Nesterov , John Hubbard , Jan Kara , "Kirill A . Shutemov" , Pavel Begunkov , Mika Penttila , Dave Chinner , Theodore Ts'o , Peter Xu References: <7d56b424-ba79-4b21-b02c-c89705533852@lucifer.local> <1d4c9258-9423-7411-e722-8f6865b18886@linux.ibm.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <1d4c9258-9423-7411-e722-8f6865b18886@linux.ibm.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. -- Thanks, David / dhildenb