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[2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id u19-20020a05600c00d300b003f17eaae2c9sm35746626wmm.1.2023.05.02.06.47.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 06:47:45 -0700 (PDT) Message-ID: Date: Tue, 2 May 2023 15:47:43 +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 . 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Shutemov" , Pavel Begunkov , Mika Penttila , Dave Chinner , Theodore Ts'o , Peter Xu References: <7d56b424-ba79-4b21-b02c-c89705533852@lucifer.local> From: David Hildenbrand Organization: Red Hat In-Reply-To: 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: 8bit X-Rspam-User: X-Stat-Signature: ss36wegxwg9ee6nngdtkb631w7ang1ei X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 57CAD418EB X-HE-Tag: 1683035323-934611 X-HE-Meta: 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 +lqI8+ei HaHvVK7fVgconvqm/hYpLWvMRX0QhsEuHTUV0g7gpBmI9Te0CLxVhgJNBBQbV0MSQYQog7KYIsqSGCI7/gfLtMqw3mc0z+NBjaLXKE0+5rI/pbhzaqxVkuR8yBjUP0QFIn+3bgE6VolnGQLwjenzQM1di/GREJGMFOk95p78nh/Jk/ePDtXNbr7L45BkAY8SgXhEphGF6X2BAUsIGdkoSnbXUNSA6/oUNfGuC47ABJYtEH1PvOQxONcJTFw== 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 15:43, Matthew Rosato wrote: > On 5/2/23 9:39 AM, David Hildenbrand wrote: >> On 02.05.23 15:36, Jason Gunthorpe wrote: >>> On Tue, May 02, 2023 at 03:28:40PM +0200, 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 >>>>>>     >>>>>>       >>>>>>     >>>>> >>>>> 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] >>> >>> Not upstream they aren't. >>> >>>> Well, zPCI is special. I cannot immediately tell when we would trigger >>>> long-term pinning. >>> >>> zPCI uses the standard IOMMU stuff, so it uses a normal VFIO container >>> and the normal pin_user_pages() path. >> >> >> @Christian, Matthew: would we pin all guest memory when starting the domain (IIRC, like on x86-64) and fail early, or only when the guest issues rpcit instructions to map individual pages? >> > > 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. > However, per Jason's prior suggestion, the initial implementation for s390 nesting via iommufd will pin all of guest memory when starting the domain. I have something already working via iommufd built on top of the nesting infrastructure patches and QEMU iommufd series that are floating around; needs some cleanup, hoping to send an RFC in the coming weeks. I can CC you if you'd like. Yes, please. -- Thanks, David / dhildenb