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See http://www.infradead.org/rpr.html X-Rspamd-Queue-Id: C6ACA4001B X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: n483yeax8xsjnog1ce9cnmojwtcuny6h X-HE-Tag: 1685089091-167419 X-HE-Meta: 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 3aMGhnD8 bM9P6FYtGL+9ybqCN4BTtN3Vna0Wts+i4dNpqBEf3vBfknH9ZyRi0XpiTakJnjg130Dqqo4xiedXWEb+dJFp7ufNti+JdZ0CTJmi4IcLWf6Up4JLBasR87N9zw8YaqcfN6LPK7O2aQKH1LFYGDQY8H4nRUYZTtgpQj8cR+VIEJIL1B0ZC6UDuQv9tpAtVzdyyPQ2OKHiinKVN70crmLKnSaTyGkTrIc7VjvjWD3JnLsS9YvvOKVr8N/W0pWAi0WHlFVRBj79aiVPlrqMPSFb3/aRKJLB4/YarvlQ4tcd2YUpx5Iz4xT8bNhC6i48vNF0zdoLXC6CeYmFhjVmI5mFH5ke2DqqSCyOZZ9rbVXodi+RXVkFiWE9QpmtcK+ml7fyJlJrCgSTmmBe5+N1p6EXze2/Nt3iCef4TJ6r91xlyOMJNthJs3Xgs4ndc9Q== 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 Fri, May 26, 2023 at 09:10:33AM +0100, Lorenzo Stoakes wrote: > On Thu, May 25, 2023 at 11:39:51PM +0100, David Howells wrote: > > Make pin_user_pages*() leave a ZERO_PAGE unpinned if it extracts a pointer > > to it from the page tables and make unpin_user_page*() correspondingly > > ignore a ZERO_PAGE when unpinning. We don't want to risk overrunning a > > zero page's refcount as we're only allowed ~2 million pins on it - > > something that userspace can conceivably trigger. > > I guess we're not quite as concerned about FOLL_GET because FOLL_GET should > be ephemeral and FOLL_PIN (horrifically) adds GUP_PIN_COUNTING_BIAS each > time? I think FOLL_GET would be just as useful. But given that we have a few places that release pins while gets just do a put_page it would be a lot more effort to audit all of them. Maybe it's better do only do this once we've converted all the places that should do pin and have very few FOLL_GET users left.