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[89.27.86.246]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e254f02f1sm3413741f8f.3.2026.10.20.23.05.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 23:05:56 -0700 (PDT) From: mpenttil@redhat.com To: linux-mm@kvack.org Cc: dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-kernel@vger.kernel.org, =?UTF-8?q?Mika=20Penttil=C3=A4?= , David Hildenbrand , Jason Gunthorpe , Leon Romanovsky , Alistair Popple , Balbir Singh , Zi Yan , Matthew Brost , Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Lyude Paul , Danilo Krummrich Subject: [PATCH v16 11/12] Documentation/mm/hmm: document migration through hmm_range_fault() Date: Wed, 21 Oct 2026 09:05:05 +0300 Message-ID: <20261021060506.2377545-12-mpenttil@redhat.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261021060506.2377545-1-mpenttil@redhat.com> References: <20261021060506.2377545-1-mpenttil@redhat.com> X-Archived-By: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: VNArv0ntEofwag9C3T7VIp-Y6S_cP2z6qWSz-C5hK_4_1792562759 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CE8AD140003 X-Rspam-User: X-Stat-Signature: z5q4hobi5q536k7o7ajwffe4sjrbihzx X-Spam-Status: No, score=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1792562763-269201 X-HE-Meta: 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 qw5xKcCe GeRzKog3YlzaphoM6EpwVm3Dozfr6NaX/s1hyJGJCC8mfOMq8DUE1V5zV7rJUQnw7d8arrYy3wjtgcdd19WQo1KByyXDUA1YM5B+PsrBnw/hylmJZspXbtFLtN7K78v0qYHWprbDUawKXSduFFMAqcQCZgVvAgrNb3B9nvmwAKRpq41qoiccmV8185b64QzoTL4rhf0x1ZILhxIDfJfeZVrBr1WiRDraye/eV3g9r4Lk0DLZ0WjH5SrrWqIs939khIguW0PNGADwC0f/hwgiFweJJt+piB+fPnJ5JjWqTJXvqh7Htk4afIpbOg+qjZoyXZjeDpz/oqq2I4lhnZHBIFpJRiS3CjLhIUArX4ejM9bqyDUf+Zfnvhjm0T8wREzlfE0j+VoXb5LcHhi4JKtIP6ctv3JN4aqzlTuHqPCD7DN80zEkvxeY3U2OlDxMMMbUDmYb8p4NWKgmOoYW0L5on32yMQw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 From: Mika Penttilä Describe the two new MIGRATE_VMA_FAULT / MIGRATE_VMA_WRITE flags of migrate_vma_setup(), and add a section on driving the migration collection phase directly from hmm_range_fault() via HMM_PFN_REQ_MIGRATE and migrate_hmm_range_setup(). Signed-off-by: Mika Penttilä --- Documentation/mm/hmm.rst | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/Documentation/mm/hmm.rst b/Documentation/mm/hmm.rst index fc1b8dc19825..58424e5f5873 100644 --- a/Documentation/mm/hmm.rst +++ b/Documentation/mm/hmm.rst @@ -348,6 +348,13 @@ between device driver specific code and shared common code: Currently only anonymous private VMA ranges can be migrated to or from system memory and device private memory. + By default only pages already present are collected. Two additional flags + ask migrate_vma_setup() to fault in missing pages first: + + * ``MIGRATE_VMA_FAULT`` faults in missing pages with read access. + * ``MIGRATE_VMA_WRITE`` faults in missing pages with write access + (implies faulting). + One of the first steps migrate_vma_setup() does is to invalidate other device's MMUs with the ``mmu_notifier_invalidate_range_start()`` and ``mmu_notifier_invalidate_range_end()`` calls around the page table @@ -427,6 +434,38 @@ between device driver specific code and shared common code: The lock can now be released. +Migration collection through hmm_range_fault() +============================================== + +The collection phase of migration (steps 1 and 2 above) can also be driven by +hmm_range_fault() directly, sharing its page table walk. This lets a driver +fault in and collect a range for migration in one walk, which is useful for +migrate on fault. + +To do so, the driver sets ``HMM_PFN_REQ_MIGRATE`` in ``range->default_flags`` +and points ``range->migrate`` at a ``struct migrate_vma`` it has filled in +(``flags``, ``src``, ``dst``, ``pgmap_owner``). Usually ``HMM_PFN_REQ_FAULT`` +(and ``HMM_PFN_REQ_WRITE``) is set as well, so missing pages are faulted in +before being collected. The mmap_read_lock() has to be held for the whole +migration, since the vma must stay stable. + +hmm_range_fault() collects the entries the same way migrate_vma_setup() does, +taking a folio reference, locking it and installing a migration PTE. Collected +entries are marked with ``HMM_PFN_VALID | HMM_PFN_MIGRATE`` in +``range->hmm_pfns``. If the page tables change while locks are dropped the +partially collected entries are rolled back automatically. + +After hmm_range_fault() returns, the driver calls:: + + void migrate_hmm_range_setup(struct hmm_range *range); + +to translate ``range->hmm_pfns`` into ``migrate->src[]`` (``migrate->dst[]`` is +zeroed) and initialize ``migrate->cpages`` and ``migrate->npages``. From here on +the ``range->migrate`` struct is ready for the rest of the flow (steps 3 +onwards), i.e. migrate_vma_pages() and migrate_vma_finalize(). This should be +called even on error, since hmm_range_fault() may have collected part of the +range before failing. + Exclusive access memory ======================= -- 2.55.0