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b=e0FGFPFZV0eKLLl32jk8I59lTEHQZEc8BJazgceNrvGoPpcwCu+4WvrvaSKgCd9WX IzOyxh5oVJv8Nwhf5GAZZMKstLdzYZ32czuXW9YbIlsF03Nm3316wrUZvZlxWKb6du 1PI+nawkxeyHD3BszZ03n5XTcheeQMbGpQFJ5Fs1Kcei/oeJBiMO3407pEVCoFxfRp w+UqDHQWXzrYlTaICvdhu1UyuH0FoWiPJyYnP7SA8hO6sA+LJGZky0dPGRW4/HJK6q FsTNGORi3mzq4nTdwM7L+t0toa2Kn+9DsarvP71ZTDicaw2OfwnPj1BKd7c89OkoOU Zl4DnismZRDgA== Message-ID: <829c448d-e6e2-4874-a166-7624e87489ef@kernel.org> Date: Wed, 28 Oct 2026 09:43:49 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] RDMA/uverbs: Don't return the shared zero page from rdma_umap_fault() To: Zi Yan , Jason Gunthorpe , Leon Romanovsky Cc: linux-mm@kvack.org, Lorenzo Stoakes , Lance Yang , Kiryl Shutsemau , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org References: <20261025-fix-rdma_umap_fault-zero-page-v1-1-186255624f1f@nvidia.com> <78802ed9-9cc6-41c4-b131-7c7d38f7ff39@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 34F64180004 X-Stat-Signature: 716ej89phskctmakudq6iwpqpy5jjioc X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1793177036-377604 X-HE-Meta: U2FsdGVkX1+Ef720S1iGsqsf7FlNi3ZQU8QYh+feVVq0u8B7T/hv5wOBN7aDB+2WOg2rmDRGZ6jFXe6aE/UNYQrveWsF1L6tmQ80DRWOKlqxe+krPB22LNU0X00e6WAOQs7cOud1w2rRr5fFfZObwmUyYHhVWh0IWAscM8Ls9Vh/VUkizchHvdjvpMM9Uz3UPkWpCljTNPQsbP6r7rUxcK005fbcYGQ8qfUcujy7vdNxq+CHcvfxYRtnEjj/FK7jPa/qVuxKVcHgWmy6s7Cjej2OdQu6OvRvUEPACHFxqWuwF5BxWvSuZ4z0mvy7UFg6UOHExRu+kuLpjdfu0PIb7AMGXaWeL5zh/r5tZjmGxopwwfqRm63zDvde6SdOj006Bzt1ERwzsA1cRmy6NVK81veIlTAZKu7UoOm8xex56HEY+rHDIiU3uD9ztdFPYJP9OYYA/jme4oCBfX6R2veuArbgFohGAhCP02MQX6/lb+8mtk06/sA+TTEyJES4Ea2bUXnXQ7GdSo63838xSpH6y3H/xATNiK8b0+4SkLem/nxPjPkemTXHuPOos5txfE2tE2GGslxxc6ruThiTmXlBGr5OHCxK1kusGAuZp4/0g/wOiYLi87Owi0HNO7cIE00zsQifFjab2WMvFVds+Whl18zOSAAygwiAwOD0AyNyMhHeqzkX4rcfa7kCS7DUBf1OEEk9tj1JKJN5c3bWdnM0J/U0WnK1ksHn9US6W2HGaPwHlT7o7xja7pIX6YMtggVHNl7VI6KFI8gtOWPiquP6XYQb81/w4XMr92LY1g9g3PQ616oce/S0UjR4ARcbf04AbZrRDEKeq2ILiEVc5a8k7v53r1ZLenis0Fam4OltoaE5NrC223KSCaRqyw/l5T6mWRJIJqehdQVXp9K1hkF0JG+1N/rrfVrmmf8OEhelJ1KTYs3iHK0AYd5n/VQrWLZ5paSJU8vWEtJQV2vA+we BbVg1I85 Ui7NkceBOJtmumQt9vfe4D+Dz8274v4uqfAFShmQ1wBGbF1L7vCPGo407e4E+ERKDO+4CvadFIHGtKPfluhVVHK1e7AQ85/eNc2QzYf4RwdTpskOkmMFIap8RSU51LfxUBEaz0p2WG9IUNWfVY7rsjRfNzLeadOv73YdKFqK0gOhj2twr8/djulC8F8aOC4hfksBucRfGiIDcnBk0TS5J0aodc5WOXeET/0Pn+PCHkmlIyRF6ALW1CgkZjlOP58gyrY3rukY9BuT3U0cezW1tDgDD5oGZPwlWPmBTEuYtT7cmnxK59aWjoZCqfw== 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 >>> + /* >>> + * VMAs that cannot become writable map the page as a raw pfn, like >>> + * the device memory it replaces. The page lives as long as the file. >>> + */ >>> + if (!(vmf->vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) { >>> + ret = vmf_insert_pfn(vmf->vma, vmf->address, page_to_pfn(page)); >>> + goto out; >>> + } >>> + >>> + /* >>> + * This VMA is forced to always be shared so this doesn't have >>> + * to worry about COW. >>> + */ >>> + vmf->page = page; >>> + get_page(page); >> >> >> This split handling is pretty horrible TBH. >> >> In once case we take a reference in the other not? >> >> Why not perform a PFN mapping in any case? > > For writable path, a new vmf_insert_pfn_mkwrite() is needed, so it was > not fixed. I can fix that part as well. We should do that; returning kernel allocations from this function in ->fault is bad. How urgent is this fix here? (can it actually be triggered?Specific hardware?) > > The read-only zero page part might need more attention, since > we just prevented vmf_insert_pfn_prot() from using zero_page. Do we want > to add the support for rdma_umap_fault()? We just have to make sure that we cannot install it writable etc. But that's not a concern. Just have to be careful :) > >> >> (Does GUP have to work on these things?) > > These are VM_PFNMAP mappings, I guess not. But I am not a GUP expert. So we installed folios with ->fault in VM_PFNMAP!?!?!?! That doesn't sound right :) -- Cheers, David