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Howlett" , Nikita Kalyazin , Lorenzo Stoakes , David Hildenbrand , Mike Rapoport , Suren Baghdasaryan , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Vlastimil Babka , Muchun Song , Hugh Dickins , Andrew Morton , James Houghton , Michal Hocko , Andrea Arcangeli , Oscar Salvador , Axel Rasmussen , Ujwal Kundur Subject: Re: [PATCH v2 1/4] mm: Introduce vm_uffd_ops API Message-ID: References: <982f4f94-f0bf-45dd-9003-081b76e57027@lucifer.local> <289eede1-d47d-49a2-b9b6-ff8050d84893@redhat.com> <930d8830-3d5d-496d-80d8-b716ea6446bb@amazon.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: Fjb3RFBcvCwo2b6Up8KBC_UTnybvjXghgA9cSkJ4Jm4_1758053135 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 8D87540003 X-Stat-Signature: 59ygrhh7mxyaitf1xxjrm5i1aobqkmq6 X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1758053137-488167 X-HE-Meta: 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 sKuzBDx3 VrrXkL241BlfzVMWES6Ptk0yf2C7eZ0kJKYvqlalzBqpLG6OKlZoC4uL90NpD9x53mFWz6zQ2W7meLqmcnYq/BkGDlrzVOtyekxNja36PJIfymytxrx9sNr0WYA+AdLGX6lfGLzT9zfJw5x51ekwtw6V6Op/KW5+MAi7cFNFeUjJzuMv/MeekbirqVKo+nIDtCpXFXP892dChVPLGE//wEao3yLHT4J+o91wS8lYZMGmX3dZs5/KLJvXvhtt1SymFM/2j3ccxNvkS++laB0bL4KGirtsifKTTaNcYQRpB1DGfn9V7DHcIindiofTrs6HXfn2o3T2YL/1rOHWKhQM2OLNcHkSj8SobPHzIGPb12TVJycDXOU8Scyte2tZz0P1WFMcXEjQCRnng9f8kfi0EFLeVb3iocRV3soe3XQM5B+MJpP8PHM3L5bKCjmsg8kY0kAfkIuWApzx7FCo= 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: On Mon, Sep 08, 2025 at 12:53:37PM -0400, Liam R. Howlett wrote: > What we don't want is non-mm code specifying values for the function > pointer and doing what they want, or a function pointer that returns a > core mm resource (in the old example this was a vma, here it is a > folio). > > From this patch set: > + * Return: zero if succeeded, negative for errors. > + */ > + int (*uffd_get_folio)(struct inode *inode, pgoff_t pgoff, > + struct folio **folio); > > This is one of the contention points in the current scenario as the > folio would be returned. OK I didn't see this one previously, it partly answers one of my question in the other reply, in a way I wished not. Could you elaborate why an API returning an folio pointer would be dangerous? OTOH, would you think alloc_pages() or folio_alloc() be dangerous too? They return a folio from the mm core to drivers, hence it's not the same direction of folio sharing, however it also means at least the driver can manipulate the folio / memmap as much as it wants, sabotaging everything is similarly possible. Why we worry about that? Are we going to unexport alloc_pages() someday? Thanks, -- Peter Xu