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[2003:d8:2f20:7500:5f99:9633:990e:138]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4589ee628fcsm66571965e9.31.2025.08.01.07.13.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Aug 2025 07:13:37 -0700 (PDT) Message-ID: <286466e3-9d1c-40a0-a467-a48cb2b657b4@redhat.com> Date: Fri, 1 Aug 2025 16:13:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/userfaultfd: fix missing PTE unmap for non-migration entries From: David Hildenbrand To: Sasha Levin Cc: Andrew Morton , peterx@redhat.com, aarcange@redhat.com, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250630031958.1225651-1-sashal@kernel.org> <20250630175746.e52af129fd2d88deecc25169@linux-foundation.org> <214e78a0-7774-4b1e-8d85-9a66d2384744@redhat.com> <593b222e-1a62-475c-9502-76e128d3625d@redhat.com> Autocrypt: addr=david@redhat.com; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAmgsLPQFCRvGjuMACgkQTd4Q 9wD/g1o0bxAAqYC7gTyGj5rZwvy1VesF6YoQncH0yI79lvXUYOX+Nngko4v4dTlOQvrd/vhb 02e9FtpA1CxgwdgIPFKIuXvdSyXAp0xXuIuRPQYbgNriQFkaBlHe9mSf8O09J3SCVa/5ezKM OLW/OONSV/Fr2VI1wxAYj3/Rb+U6rpzqIQ3Uh/5Rjmla6pTl7Z9/o1zKlVOX1SxVGSrlXhqt kwdbjdj/csSzoAbUF/duDuhyEl11/xStm/lBMzVuf3ZhV5SSgLAflLBo4l6mR5RolpPv5wad GpYS/hm7HsmEA0PBAPNb5DvZQ7vNaX23FlgylSXyv72UVsObHsu6pT4sfoxvJ5nJxvzGi69U s1uryvlAfS6E+D5ULrV35taTwSpcBAh0/RqRbV0mTc57vvAoXofBDcs3Z30IReFS34QSpjvl Hxbe7itHGuuhEVM1qmq2U72ezOQ7MzADbwCtn+yGeISQqeFn9QMAZVAkXsc9Wp0SW/WQKb76 FkSRalBZcc2vXM0VqhFVzTb6iNqYXqVKyuPKwhBunhTt6XnIfhpRgqveCPNIasSX05VQR6/a OBHZX3seTikp7A1z9iZIsdtJxB88dGkpeMj6qJ5RLzUsPUVPodEcz1B5aTEbYK6428H8MeLq NFPwmknOlDzQNC6RND8Ez7YEhzqvw7263MojcmmPcLelYbfOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCaCwtJQUJG8aPFAAKCRBN3hD3AP+DWlDnD/4k2TW+HyOOOePVm23F5HOhNNd7nNv3 Vq2cLcW1DteHUdxMO0X+zqrKDHI5hgnE/E2QH9jyV8mB8l/ndElobciaJcbl1cM43vVzPIWn 01vW62oxUNtEvzLLxGLPTrnMxWdZgxr7ACCWKUnMGE2E8eca0cT2pnIJoQRz242xqe/nYxBB /BAK+dsxHIfcQzl88G83oaO7vb7s/cWMYRKOg+WIgp0MJ8DO2IU5JmUtyJB+V3YzzM4cMic3 bNn8nHjTWw/9+QQ5vg3TXHZ5XMu9mtfw2La3bHJ6AybL0DvEkdGxk6YHqJVEukciLMWDWqQQ RtbBhqcprgUxipNvdn9KwNpGciM+hNtM9kf9gt0fjv79l/FiSw6KbCPX9b636GzgNy0Ev2UV m00EtcpRXXMlEpbP4V947ufWVK2Mz7RFUfU4+ETDd1scMQDHzrXItryHLZWhopPI4Z+ps0rB CQHfSpl+wG4XbJJu1D8/Ww3FsO42TMFrNr2/cmqwuUZ0a0uxrpkNYrsGjkEu7a+9MheyTzcm vyU2knz5/stkTN2LKz5REqOe24oRnypjpAfaoxRYXs+F8wml519InWlwCra49IUSxD1hXPxO WBe5lqcozu9LpNDH/brVSzHCSb7vjNGvvSVESDuoiHK8gNlf0v+epy5WYd7CGAgODPvDShGN g3eXuA== Organization: Red Hat In-Reply-To: <593b222e-1a62-475c-9502-76e128d3625d@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cNz3k_cFIily3im-eSHZdtiVGSg-h2WmJ_WtnLqFxaY_1754057619 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 02821180010 X-Stat-Signature: cuy9yxerci3gtbi6ofc3b1wxb6wzsw6p X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1754057621-93873 X-HE-Meta: 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 vEoRmlTo NKEmA3FCY/3DQREW3tsiO3FZJKiu/GGGkrIxRiaBzFgOgpE2EogCUbA62i29P8cr1RrX1eGIcppZz5YjS+3Z3IhFb68EwuWWAi7mJ07yC+bxn0OyTN1v0wrR5I68ePat5+FPQbIsJMjN+m8hHaHRkxJA9f7N/Woz9YDwiu5YDQaKC7EgQEOZIVJ7mChG/4mcppE0XuuT2VqQvp7KPQNI64BxfEHF3ErEYAM+GUziLkkWnIsq2yHyB/YDD+sGpl6/PSBJQo9y5ksj6pjEAgq6AfPi4q2CDzstPSN6il4bjYVHd+qaAdCGEam8nMdkYFMaxYd2CxTcraBJANz73aL7eknGppIaJ7LSNiUGWjuXNJc9pVbjPMDN06yG+dmj1xRazb5sgu5oz8Tn6LF+gBi2wSEFoBcP1iFGj4foTCoGtwe0wxJFE3u2QH9MlXpVmXkB4wp4Ctw6Op2hctinjMSXHJ5lJL7HjO6BDKUKA 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 01.08.25 16:06, David Hildenbrand wrote: > On 01.08.25 15:26, Sasha Levin wrote: >> On Thu, Jul 31, 2025 at 02:56:25PM +0200, David Hildenbrand wrote: >>> On 31.07.25 14:37, Sasha Levin wrote: >>>> On Tue, Jul 08, 2025 at 05:42:16PM +0200, David Hildenbrand wrote: >>>>> On 08.07.25 17:33, Sasha Levin wrote: >>>>>> On Tue, Jul 08, 2025 at 05:10:44PM +0200, David Hildenbrand wrote: >>>>>>> On 01.07.25 02:57, Andrew Morton wrote: >>>>>>>> On Sun, 29 Jun 2025 23:19:58 -0400 Sasha Levin wrote: >>>>>>>> >>>>>>>>> When handling non-swap entries in move_pages_pte(), the error handling >>>>>>>>> for entries that are NOT migration entries fails to unmap the page table >>>>>>>>> entries before jumping to the error handling label. >>>>>>>>> >>>>>>>>> This results in a kmap/kunmap imbalance which on CONFIG_HIGHPTE systems >>>>>>>>> triggers a WARNING in kunmap_local_indexed() because the kmap stack is >>>>>>>>> corrupted. >>>>>>>>> >>>>>>>>> Example call trace on ARM32 (CONFIG_HIGHPTE enabled): >>>>>>>>> WARNING: CPU: 1 PID: 633 at mm/highmem.c:622 kunmap_local_indexed+0x178/0x17c >>>>>>>>> Call trace: >>>>>>>>> kunmap_local_indexed from move_pages+0x964/0x19f4 >>>>>>>>> move_pages from userfaultfd_ioctl+0x129c/0x2144 >>>>>>>>> userfaultfd_ioctl from sys_ioctl+0x558/0xd24 >>>>>>>>> >>>>>>>>> The issue was introduced with the UFFDIO_MOVE feature but became more >>>>>>>>> frequent with the addition of guard pages (commit 7c53dfbdb024 ("mm: add >>>>>>>>> PTE_MARKER_GUARD PTE marker")) which made the non-migration entry code >>>>>>>>> path more commonly executed during userfaultfd operations. >>>>>>>>> >>>>>>>>> Fix this by ensuring PTEs are properly unmapped in all non-swap entry >>>>>>>>> paths before jumping to the error handling label, not just for migration >>>>>>>>> entries. >>>>>>>> >>>>>>>> I don't get it. >>>>>>>> >>>>>>>>> --- a/mm/userfaultfd.c >>>>>>>>> +++ b/mm/userfaultfd.c >>>>>>>>> @@ -1384,14 +1384,15 @@ static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, >>>>>>>>> entry = pte_to_swp_entry(orig_src_pte); >>>>>>>>> if (non_swap_entry(entry)) { >>>>>>>>> + pte_unmap(src_pte); >>>>>>>>> + pte_unmap(dst_pte); >>>>>>>>> + src_pte = dst_pte = NULL; >>>>>>>>> if (is_migration_entry(entry)) { >>>>>>>>> - pte_unmap(src_pte); >>>>>>>>> - pte_unmap(dst_pte); >>>>>>>>> - src_pte = dst_pte = NULL; >>>>>>>>> migration_entry_wait(mm, src_pmd, src_addr); >>>>>>>>> err = -EAGAIN; >>>>>>>>> - } else >>>>>>>>> + } else { >>>>>>>>> err = -EFAULT; >>>>>>>>> + } >>>>>>>>> goto out; >>>>>>>> >>>>>>>> where we have >>>>>>>> >>>>>>>> out: >>>>>>>> ... >>>>>>>> if (dst_pte) >>>>>>>> pte_unmap(dst_pte); >>>>>>>> if (src_pte) >>>>>>>> pte_unmap(src_pte); >>>>>>> >>>>>>> AI slop? >>>>>> >>>>>> Nah, this one is sadly all me :( >>>>> >>>>> Haha, sorry :P >>>> >>>> So as I was getting nowhere with this, I asked AI to help me :) >>>> >>>> If you're not interested in reading LLM generated code, feel free to >>>> stop reading now... >>>> >>>> After it went over the logs, and a few prompts to point it the right >>>> way, it ended up generating a patch (below) that made sense, and fixed >>>> the warning that LKFT was being able to trigger. >>>> >>>> If anyone who's more familiar with the code than me (and the AI) agrees >>>> with the patch and ways to throw their Reviewed-by, I'll send out the >>>> patch. >>> >>> Seems to check out for me. In particular, out pte_unmap() everywhere >>> else in that function (and mremap.c:move_ptes) are ordered properly. >>> >>> Even if it would not fix the issue, it would be a cleanup :) >>> >>> Acked-by: David Hildenbrand >> >> David, I ended up LLM generating a .cocci script to detect this type of >> issues, and it ended up detecting a similar issue in >> arch/loongarch/mm/init.c. > > Does loongarch have these kmap_local restrictions? loongarch doesn't use HIGHMEM, so it probably doesn't matter. Could be considered a cleanup, though. -- Cheers, David / dhildenb