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[2003:cb:c705:d100:871b:ec55:67d:5247]) by smtp.gmail.com with ESMTPSA id h11-20020a1ccc0b000000b003fbdd5d0758sm13758328wmb.22.2023.08.01.05.22.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Aug 2023 05:22:13 -0700 (PDT) Message-ID: Date: Tue, 1 Aug 2023 14:22:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [RFC v1 1/3] mm/mmu_notifier: Add a new notifier for mapping updates (new pages) To: Jason Gunthorpe , "Kasireddy, Vivek" Cc: "Kim, Dongwon" , "Chang, Junxiao" , "dri-devel@lists.freedesktop.org" , Alistair Popple , Hugh Dickins , Peter Xu , "linux-mm@kvack.org" , Gerd Hoffmann , Mike Kravetz References: 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: 7bit X-Rspamd-Queue-Id: D31B040016 X-Rspam-User: X-Stat-Signature: 8w7tckzwdor11i4s8183y7yuhpzny1up X-Rspamd-Server: rspam01 X-HE-Tag: 1690892537-861340 X-HE-Meta: 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 7Ohjc4Xy wtDO/5a7uTY1BCM00xQ5zRiJPs4zeBaiMwmsHd3an1oMd4UhTLuMvfm+XhpRXtIc4Q6gDF7dtP8GueEGhwbvVZGZf3RnNyrxZH/zVfAKy03h4qE6kB6AZNlIs3ljbt32rt8J2Sj43yb7s9CIo+aBsndF88g0cv4h0liljC+FReNriGF+UWDFwzkqukKbT3A1mj9JhYsNCauzSmeSJxM057OP2Rb+3wJ4QFYuwhZ9eI8PCFelP8a9miVNMoToRmYb7otliQLp+pA2d2dDervw08xWAesJqz+XDmTBEnZ2j6sC8FgKjEmoCiEqPojNsl6GtOiK+xLE8RHanxIpJmuMucvoAssJ5sERwnMho5Sx4wlZKSFjRm1uoI7X7dsbbh9hWxphdf5lEKeaTYnR7oh7/evQU/OqeibyaPj6q9cmcDLTZ8jxQzfnTalvBGm4c7AqkmqVUw+n4a73k8/txzjl+163kOw== 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 01.08.23 14:19, Jason Gunthorpe wrote: > On Tue, Aug 01, 2023 at 05:32:38AM +0000, Kasireddy, Vivek wrote: > >>> You get another invalidate because the memfd removes the zero pages >>> that hmm_range_fault installed in the PTEs before replacing them with >>> actual writable pages. Then you do the move, and another >>> hmm_range_fault, and basically the whole thing over again. Except this >>> time instead of returning zero pages it returns actual writable >>> page. > >> Ok, when I tested earlier (by registering an invalidate callback) but without >> hmm_range_fault(), I did not find this additional invalidate getting triggered. >> Let me try with hmm_range_fault() and see if everything works as expected. >> Thank you for your help. > > If you do not get an invalidate then there is a pretty serious bug in > the mm that needs fixing. > > Anything hmm_range_fault() returns must be invalidated if the > underying CPU mapping changes for any reasons. Since hmm_range_fault() > will populate zero pages when reading from a hole in a memfd, it must > also get an invalidation when the zero pages are changed into writable > pages. Can you point me at the code that returns that (shared) zero page? -- Cheers, David / dhildenb