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[2003:cb:c700:2400:6b79:2aa:9602:7016]) by smtp.gmail.com with ESMTPSA id p8-20020a05600c358800b003f1738d0d13sm51382271wmq.1.2023.05.02.06.57.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 May 2023 06:57:32 -0700 (PDT) Message-ID: <1ffbbfb7-6bca-0ab0-1a96-9ca81d5fa373@redhat.com> Date: Tue, 2 May 2023 15:57:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 To: Jason Gunthorpe Cc: Matthew Rosato , 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 Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings 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: 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 15:50, 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. > > Which, again, makes it weird/wrong that this KVM code is pinning it > again :\ IIUC, that pinning is not for ordinary IOMMU / KVM memory access. It's for passthrough of (adapter) interrupts. I have to speculate, but I guess for hardware to forward interrupts to the VM, it has to pin the special guest memory page that will receive the indications, to then configure (interrupt) hardware to target the interrupt indications to that special guest page (using a host physical address). -- Thanks, David / dhildenb