From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B16AC26C3A2 for ; Fri, 1 Aug 2025 14:13:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754057624; cv=none; b=qnnl6vELfy3hmtuMe4HHe5YQ/V82MaEiT9DglYGp7I3TMaanpGD8p4ueucSWfqDQWa3mUsgpyp77a+q3VJ7LLiMTxdpnKvg486Ql3O3FayvbCWTEcsy3yhLinqkckzG8Zw2ViMDqVOsLTg8lgKYrVHmJVE38N15N1tQCAjENjDM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754057624; c=relaxed/simple; bh=kvbVEF7c9SDapc6JykRKt8pOB7KOFmfvV7rTwygDQAI=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=DOc3uDWpVli/Fz4gKvZKFsJ3NDb5+g9T86Ek7EbqtniChLja5AKVP7ebYvrYlzMgj9io0uxlCxYbjNDEhlh4YRk5ycqAND7RePT8QlZf3Yx6mimh6PKDPWjYUecPaENQt2GJuEUbmo9o2GJZpgFH3tqOampJ0BniOsSqOak7Aio= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=OO/u4c1/; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OO/u4c1/" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1754057621; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=EbFv2TD7NDloKozndUcyagdfd/67A0nNkTyyQSYo1J8=; b=OO/u4c1/RIzkLtmdXN0ce4l3cJ06MNu20FIjmDV6+ceDyWVWlVndOy9e3eL7HoRPRylDDo FHpjdAqod+jWy++LNbshv0eydf8Uoic7cHnDUw7slTnpOxvJTvowD26BryiSC7hiibZnbV mEdlt2zchqhIBb05XGnKK/7SrmDXXRQ= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-356-S6BIC-FxPdyVIFc0KLE-DQ-1; Fri, 01 Aug 2025 10:13:40 -0400 X-MC-Unique: S6BIC-FxPdyVIFc0KLE-DQ-1 X-Mimecast-MFC-AGG-ID: S6BIC-FxPdyVIFc0KLE-DQ_1754057619 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-3b78a034d25so1666221f8f.0 for ; Fri, 01 Aug 2025 07:13:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1754057619; x=1754662419; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:references:cc:to:from:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=EbFv2TD7NDloKozndUcyagdfd/67A0nNkTyyQSYo1J8=; b=mI639GFFk6SgyQlQrVQQagULmASvvCSVRtt6y7lmpy1nxKmezJ/E+9UUr7/wm+KHko w1H8YS8miRJP6BxESPxD5rXQ4dPt5jeaM5SZw+suf63TRkLlspgqVp1RzB7+RiiqziOx BARh8mL46YPJaT/lTKjrKds1pzQ0fZdnXxzXWktxE9aH49aL7GdL/bTmeXoxkRBlSfI6 tJUXiJk91idwKT1qmMG0GdueNyc22hP3ebvX4DCozxGVfgh0tb/vVDPyYhWiC9ywSsDi XhLVuc9RIamCtrE4adAGBZxDiWh/sL1K4wQWhO+DO2XPsq7JNrZ9RgA5WmIjSQIXhIYf XsXg== X-Forwarded-Encrypted: i=1; AJvYcCUxmUYDUpGd9/SMgGjpktXaFEHxCEbmjpt5rlX33F4GRSMbrdEtSHXDuGbpB4MFNqbQQBw9yjc=@vger.kernel.org X-Gm-Message-State: AOJu0YwX5/LFy+vcxQ+IGQPoMu1irnkvm43tBDzNAIH9XwCwkqwVI9i6 S4ZhCMw4jET4bCoxH5mD558nK0JH5ymiOJuycBpNqcoiAiS7ErweP3znIVuSflRg1y2fejPee5S sk5HIGw/fNOaKd9xwmtsLLE7ywuox4u0C//Y6O9+zHEFGLvenevUKQw6N5Q== X-Gm-Gg: ASbGncsG59nIUXYNxfedveFD3a7kzo86KczhlDuZ3qtb0wuwzXKmw9C9R53ao4o+CZB KNbobloRNwDuel3fCRNU8ER1+Z1+nrSmoIwnpdi6nvX3FQSQRV3S7UzroxxfQQNsVSF8JYsLr2L nNJ20IEKa2estoryNJ9U0YYc25Gg08tGPuJb6hpZBDyVL0J6gFMHDbYYQdbe0E68wMgn8YRQ1b6 T24vHgLUUl832TZCK/rDfmOf/bJaNYmKUhLphkuFRk0XQG/Z/CFzVrqiiNIT0XFdZCpybFynfHw 7cn9maqTips+/CKv7X9lY7JPAPIFydEsqXCfz2xax72K5GYNj/RoPDVR8ujtOVlDHUnjhH20kO2 7eEMbXYgrP2CFrRrvE86i4dEWoThTi+PcnTtxYkDdTRVECJphYZm4mqon3PjVKBr8 X-Received: by 2002:a05:6000:401f:b0:3b7:76e8:ba1e with SMTP id ffacd0b85a97d-3b794fe4fe6mr9647138f8f.11.1754057618875; Fri, 01 Aug 2025 07:13:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHJTKNrIL7Q9PR+TZ1c1/4AnaNhnzCQk8bo5y4cNtdcfLm5Ah+gjARoH1ht5K9SxH9oWHUnAg== X-Received: by 2002:a05:6000:401f:b0:3b7:76e8:ba1e with SMTP id ffacd0b85a97d-3b794fe4fe6mr9647105f8f.11.1754057618361; Fri, 01 Aug 2025 07:13:38 -0700 (PDT) Received: from ?IPV6:2003:d8:2f20:7500:5f99:9633:990e:138? (p200300d82f2075005f999633990e0138.dip0.t-ipconnect.de. [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 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> Content-Language: en-US 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> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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