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b=HL/XciLRn2tWpwwLLrUJl0MVaUmqH+DsJ3qccRi03nf4Pd24xS17o7ct81jnxMoRa CGLYLax5txB8YcN4JV7kFYIuxLu+sZIOExdpF2HwQVkVfFghNtlZ2O30DnSu4B6tzW Hm0zPBxxdYYFg6aBgZtmpv/x0l4tRlKMinyFhc09gK94gf7GUar32ygwA0iuMI9ZPE nQIrerybF1GR8oFAwx7ioyXS+cXXiSxmeDP1x+/fkDjhSdEdk5aZkNThsFao+EGdI8 yftOFqss3J7a7J/zoSbg88XCRxZVWr86wk1BqOwud6QzcMw+O3lvE6KPvugPeSNj0m P+1pwxzfL9vgw== Message-ID: <78802ed9-9cc6-41c4-b131-7c7d38f7ff39@kernel.org> Date: Mon, 26 Oct 2026 13:20:25 +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> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20261025-fix-rdma_umap_fault-zero-page-v1-1-186255624f1f@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: CDFBD4000E X-Spam-Status: No, score=-17.6 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_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Stat-Signature: fp5iho1fjzft6fg7kz1f781c3ddnqzz7 X-HE-Tag: 1793017231-345832 X-HE-Meta: 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 apebrhFM qoA5bvXGfvM4ELPTId7bcH689CBKw5YQR49zuOLMA0otgz2I9d3P5caILipPZ7p5YXdlYpz/yfpzG0PP3uv9sxRoB+ItlXjgOwuyx0Nz0NTy4bi1Sa53h2zKBLLoznEmF7MtiBJYciHLJTFQN5HbJSfPTtAcBEp7OBKuLLH3Abj/2ExTBn6NSOIxpe8z5jUHDPs+wCsXeqoodzU4qlCXvPX4s8XBHH8OUPx9AlrsgZD9hz39oOhcxm3EE4oWheAK4Zs1cwwjIbPmR9b1WoSLvoomdle/SfKvMK7ZCftYYmHXYpv2RnrYBH/t2TDTY/1Z62n47JzDRCnBwZJdNn743sVIbQM7GpLP47BpR 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 On 10/26/26 03:04, Zi Yan wrote: > After disassociation, rdma_umap_fault() returns the shared zero page from > ->fault for VMAs without VM_WRITE and VM_MAYWRITE. Such VMAs come from > rdma_user_mmap_io() in drivers that clear VM_MAYWRITE and they are shared > VM_PFNMAP. A page returned from ->fault is mapped as a normal page and goes > through rmap code. Two issues: > > 1. shared zero page causes VM_WARN_ONs in rmap code, > > 2. normal pages in shared VM_PFNMAP VMAs cause accounting leak on arch > without pte_special(), namely the page refcount, mapcount, and vm stats > are never dropped. > > Map ufile->disassociate_page for VMAs without VM_WRITE and VM_MAYWRITE, > with vmf_insert_pfn(). The page lives until ib_uverbs_release_file(), which > cannot run while a VMA holds a reference to the file. > > Writable VMAs keep returning disassociate_page in vmf->page, thus its > accounting leak on arch without pte_special() needs a separate fix. > > Userspace can see two differences after the patch. A mapping without > VM_WRITE and VM_MAYWRITE now reads what was written through writable > mappings of the same uverbs file instead of zeroes; after disassociation > both are dummy data. The first fault now allocates the page and fails with > VM_FAULT_SIGBUS if the allocation fails, as a write fault already does. > > Fixes: 67f269b37f9b ("RDMA/ucontext: Fix regression with disassociate") > Signed-off-by: Zi Yan > --- > The issue was discovered during PG_folio development when making sure only > rmappable folios can enter rmap code path. > > Alternative: map the zero page with vmf_insert_pfn_prot() > === > > Read-only mappings could keep reading zeroes if rdma_umap_fault() > installed the zero page itself as a special PTE: > > return vmf_insert_pfn_prot(vmf->vma, vmf->address, zero_pfn(vmf->address)); > > It does not work today. Commit 7b466529307be ("mm: disallow raw PFN > mappings of huge/shared zeropage") makes vmf_insert_pfn_prot() return > VM_FAULT_SIGBUS for the zero pfn. vmf_insert_mixed() does not support > VM_PFNMAP, since vm_mixed_zeropage_allowed() warns on VM_PFNMAP. > > The first version of that patch [1] did not change vmf_insert_pfn_prot(). > Due to no in-kernel user at that time and complication it can cause, > vmf_insert_pfn_prot() rejects zero pages now. > > Fix to writable VMA path > === > A new vmf_insert_pfn_mkwrite() is needed, since vmf_insert_pfn() has a > narrow failing scenario. When a process mapping the disassociated page has > soft-dirty tracking enabled, vm_page_prot becomes read-only; > vmf_insert_pfn() then uses a read-only PTE instead of a writable one; > fixup_user_fault() is used to write to the page (e.g., KVM with the uverbs > mapping as guest memory) and fails, because it does not take the second > fault to upgrade the read-only PTE to a writable one. > > LLM was used for investigation and code development. > > [1] https://lore.kernel.org/all/20260917121010.60966-1-lance.yang@linux.dev/ > --- > drivers/infiniband/core/uverbs_main.c | 44 ++++++++++++++++++++++------------- > 1 file changed, 28 insertions(+), 16 deletions(-) > > diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c > index 2a046c888dfab..c3638bf031b15 100644 > --- a/drivers/infiniband/core/uverbs_main.c > +++ b/drivers/infiniband/core/uverbs_main.c > @@ -725,39 +725,51 @@ static void rdma_umap_close(struct vm_area_struct *vma) > > /* > * Once the zap_special_vma_range has been called touches to the VMA will come here and > - * we return a dummy writable zero page for all the pfns. > + * we map a dummy page for all the pfns. > */ > static vm_fault_t rdma_umap_fault(struct vm_fault *vmf) > { > struct ib_uverbs_file *ufile = vmf->vma->vm_file->private_data; > struct rdma_umap_priv *priv = vmf->vma->vm_private_data; > vm_fault_t ret = 0; > + struct page *page; > > if (!priv) > return VM_FAULT_SIGBUS; > > - /* Read only pages can just use the system zero page. */ > - if (!(vmf->vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) { > - vmf->page = ZERO_PAGE(vmf->address); > - get_page(vmf->page); > - return 0; > - } > - > mutex_lock(&ufile->umap_lock); > if (!ufile->disassociate_page) > ufile->disassociate_page = > alloc_pages(vmf->gfp_mask | __GFP_ZERO, 0); > > - if (ufile->disassociate_page) { > - /* > - * This VMA is forced to always be shared so this doesn't have > - * to worry about COW. > - */ > - vmf->page = ufile->disassociate_page; > - get_page(vmf->page); > - } else { > + page = ufile->disassociate_page; > + if (!page) { > ret = VM_FAULT_SIGBUS; > + goto out; > + } > + > + /* Make sure the page is usable, like what __do_fault() does */ > + if (PageHWPoison(page)) { > + ret = VM_FAULT_HWPOISON; > + goto out; > } Is that really required? memory_failure() complains pretty hard on pages it doesn't know how to handle (random kernel memory). I'd assume that this here is not an ordinary pagecache page that mamoery_failure would know how to handle? > + > + /* > + * 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? (Does GUP have to work on these things?) -- Cheers, David