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[2003:cb:c747:ff00:9d85:4afb:a7df:6c45]) by smtp.gmail.com with UTF8SMTPSA id ffacd0b85a97d-390cd86cc3csm5704848f8f.33.2025.02.26.05.23.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Feb 2025 05:23:04 -0800 (PST) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, David Hildenbrand , Andrew Morton , =?UTF-8?q?J=C3=A9r=C3=B4me=20Glisse?= , Simona Vetter , Alistair Popple , Jason Gunthorpe Subject: [PATCH v2 4/5] mm/memory: document restore_exclusive_pte() Date: Wed, 26 Feb 2025 14:22:56 +0100 Message-ID: <20250226132257.2826043-5-david@redhat.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250226132257.2826043-1-david@redhat.com> References: <20250226132257.2826043-1-david@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: XhFp6dk8K0YP6Ret6Y0JWK02-ALxLjeEXImSc_K0ea4_1740576186 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspamd-Queue-Id: D463EA0027 X-Stat-Signature: 8qjgp1h1fhkzx4rnmp46s91jkz89nd4g X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1740576188-372417 X-HE-Meta: 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 uj7y2ks3 gVYZV0Ke9WQf6IdOsy/XbrkySAWR1nk9khj3khJhI07EIpyVN+HE42m8/bqYhJl6Z0MlHGV06Ce1DxvK7AfXx1pTbxTqlK72g0eBHNkbmFUvh6ArF1e5g8IZ7y8EjXkaJBR2hOeMofelsgGQ5jMgrb1mdA8LgDSJYUqWvNlX4n0J1I9XZarVpVfNXpj32RZAEAyXfMWRHYDh1AuwsGMMmibRHBFcmA5Ig3f/p6HwFvmEhJM6OMQPRh01AFtRqV0dUbMaH1ORr2MwxMa/7MJRHbq6i0x+pJ06cqB4Q4hmVhKLS7Z+vso2QkIVBjhoU98FjN8C6RaCUzv8eaCJJbZqecv/LCdyg2e3q1YasewUX1fHEb5JjGEW6yNr77JkNActGOmvrZe0yjzsFxYxTZvJh62DliD3YQjATP1ckmyWNMtyU9+LL2E4+HFIkilVMealzmL5g/ecPiO9whBNGPxW3xj3hf8SpXZ++ThYU/2f819oa6EIRAQ5rF33ZDUvHGP33941FCLdST83RSMIav9TVtDYHpo7SJ/dM2ZOb+xPc3neP2UWNT8hxxdt4xDQF4nm2ajfTlNbeBEMeGYZpfnbzupgMC9kMPz8VtrwSg2iwi951uF+RrE4Nk4nanXEXNqlmHio+jvJZaG/FjHE= 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: List-Subscribe: List-Unsubscribe: Let's document how this function is to be used, and why the folio lock is involved. Signed-off-by: David Hildenbrand --- mm/memory.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/mm/memory.c b/mm/memory.c index 2a0b4dd858769..50a305d7efcb9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -718,6 +718,32 @@ struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma, } #endif +/** + * restore_exclusive_pte - Restore a device-exclusive entry + * @vma: VMA covering @address + * @folio: the mapped folio + * @page: the mapped folio page + * @address: the virtual address + * @ptep: pte pointer into the locked page table mapping the folio page + * @orig_pte: pte value at @ptep + * + * Restore a device-exclusive non-swap entry to an ordinary present pte. + * + * The folio and the page table must be locked, and MMU notifiers must have + * been called to invalidate any (exclusive) device mappings. + * + * Locking the folio makes sure that anybody who just converted the pte to + * a device-exclusive entry can map it into the device to make forward + * progress without others converting it back until the folio was unlocked. + * + * If the folio lock ever becomes an issue, we can stop relying on the folio + * lock; it might make some scenarios with heavy thrashing less likely to + * make forward progress, but these scenarios might not be valid use cases. + * + * Note that the folio lock does not protect against all cases of concurrent + * page table modifications (e.g., MADV_DONTNEED, mprotect), so device drivers + * must use MMU notifiers to sync against any concurrent changes. + */ static void restore_exclusive_pte(struct vm_area_struct *vma, struct folio *folio, struct page *page, unsigned long address, pte_t *ptep, pte_t orig_pte) -- 2.48.1