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[2003:cb:c713:3200:77d:8652:169f:b5f7]) by smtp.gmail.com with ESMTPSA id v12-20020a05600c444c00b00412b9e4af05sm5160814wmn.0.2024.03.01.02.57.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 01 Mar 2024 02:57:17 -0800 (PST) Message-ID: <97d53a8b-1b8c-47a7-977f-4fc4977ef236@redhat.com> Date: Fri, 1 Mar 2024 11:57:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] vfio/type1: unpin PageReserved page To: Alex Williamson Cc: Yisheng Xie , akpm@linux-foundation.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20240226160106.24222-1-ethan.xys@linux.alibaba.com> <20240226091438.1fc37957.alex.williamson@redhat.com> <20240226103238.75ad4b24.alex.williamson@redhat.com> <20240227132556.17e87767.alex.williamson@redhat.com> <20240229150406.4d41db01.alex.williamson@redhat.com> From: David Hildenbrand 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/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz 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+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20240229150406.4d41db01.alex.williamson@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: A5C6EC0005 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: sbxwm6imtyu47mzwmnt16w8iaoe77mgb X-HE-Tag: 1709290642-263952 X-HE-Meta: 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 KMsbVdIh HrJY9XDwrOxDrKXI6f7U83XOe1R7PuYGwnF6V0cZmNfr71C5qj7GRLhN9BHJ1+mTcLZd/CdP3urTnQWTpUaaK2Sa0gymvpSge7ewgHJo9JcOM3O8KJCko49QuHS2tps7bKvRZcmRIRG4rKvyG1BgC0bbBXJ3E2AE+Eg7r 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 29.02.24 23:04, Alex Williamson wrote: > On Tue, 27 Feb 2024 13:25:56 -0700 > Alex Williamson wrote: > >> On Tue, 27 Feb 2024 11:27:08 +0100 >> David Hildenbrand wrote: >> >>> On 26.02.24 18:32, Alex Williamson wrote: >>>> On Tue, 27 Feb 2024 01:14:54 +0800 >>>> Yisheng Xie wrote: >>>> >>>>> 在 2024/2/27 00:14, Alex Williamson 写道: >>>>>> On Tue, 27 Feb 2024 00:01:06 +0800 >>>>>> Yisheng Xie wrote: >>>>>> >>>>>>> We meet a warning as following: >>>>>>> WARNING: CPU: 99 PID: 1766859 at mm/gup.c:209 try_grab_page.part.0+0xe8/0x1b0 >>>>>>> CPU: 99 PID: 1766859 Comm: qemu-kvm Kdump: loaded Tainted: GOE 5.10.134-008.2.x86_64 #1 >>>>>> ^^^^^^^^ >>>>>> >>>>>> Does this issue reproduce on mainline? Thanks, >>>>> >>>>> I have check the code of mainline, the logical seems the same as my >>>>> version. >>>>> >>>>> so I think it can reproduce if i understand correctly. >>>> >>>> I obviously can't speak to what's in your 5.10.134-008.2 kernel, but I >>>> do know there's a very similar issue resolved in v6.0 mainline and >>>> included in v5.10.146 of the stable tree. Please test. Thanks, >>> >>> This commit, to be precise: >>> >>> commit 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4 >>> Author: Alex Williamson >>> Date: Mon Aug 29 21:05:40 2022 -0600 >>> >>> vfio/type1: Unpin zero pages >>> >>> There's currently a reference count leak on the zero page. We increment >>> the reference via pin_user_pages_remote(), but the page is later handled >>> as an invalid/reserved page, therefore it's not accounted against the >>> user and not unpinned by our put_pfn(). >>> >>> Introducing special zero page handling in put_pfn() would resolve the >>> leak, but without accounting of the zero page, a single user could >>> still create enough mappings to generate a reference count overflow. >>> >>> The zero page is always resident, so for our purposes there's no reason >>> to keep it pinned. Therefore, add a loop to walk pages returned from >>> pin_user_pages_remote() and unpin any zero pages. >>> >>> >>> BUT >>> >>> in the meantime, we also have >>> >>> commit c8070b78751955e59b42457b974bea4a4fe00187 >>> Author: David Howells >>> Date: Fri May 26 22:41:40 2023 +0100 >>> >>> mm: Don't pin ZERO_PAGE in pin_user_pages() >>> >>> Make pin_user_pages*() leave a ZERO_PAGE unpinned if it extracts a pointer >>> to it from the page tables and make unpin_user_page*() correspondingly >>> ignore a ZERO_PAGE when unpinning. We don't want to risk overrunning a >>> zero page's refcount as we're only allowed ~2 million pins on it - >>> something that userspace can conceivably trigger. >>> >>> Add a pair of functions to test whether a page or a folio is a ZERO_PAGE. >>> >>> >>> So the unpin_user_page_* won't do anything with the shared zeropage. >>> >>> (likely, we could revert 873aefb376bbc0ed1dd2381ea1d6ec88106fdbd4) >> >> >> Yes, according to the commit log it seems like the unpin is now just >> wasted work since v6.5. Thanks! > > I dusted off an old unit test for mapping the zeropage through vfio and > started working on posting a revert for 873aefb376bb but I actually > found that this appears to be resolved even before c8070b787519. I > bisected it to: > > commit 84209e87c6963f928194a890399e24e8ad299db1 > Author: David Hildenbrand > Date: Wed Nov 16 11:26:48 2022 +0100 > > mm/gup: reliable R/O long-term pinning in COW mappings > > We already support reliable R/O pinning of anonymous memory. > However, assume we end up pinning (R/O long-term) a pagecache page > or the shared zeropage inside a writable private ("COW") mapping. > The next write access will trigger a write-fault and replace the > pinned page by an exclusive anonymous page in the process page > tables to break COW: the pinned page no longer corresponds to the > page mapped into the process' page table. > Now that FAULT_FLAG_UNSHARE can break COW on anything mapped into a > COW mapping, let's properly break COW first before R/O long-term > pinning something that's not an exclusive anon page inside a COW > mapping. FAULT_FLAG_UNSHARE will break COW and map an exclusive > anon page instead that can get pinned safely. > > With this change, we can stop using FOLL_FORCE|FOLL_WRITE for > reliable R/O long-term pinning in COW mappings. > > [...] > > Note 3: For users that use FOLL_LONGTERM right now without > FOLL_WRITE, such as VFIO, we'd now no longer pin the shared > zeropage. Instead, we'd populate exclusive anon pages that we can > pin. There was a concern that this could affect the memlock limit > of existing setups. > > For example, a VM running with VFIO could run into the memlock > limit and fail to run. However, we essentially had the same > behavior already in commit 17839856fd58 ("gup: document and work > around "COW can break either way" issue") which got merged into > some enterprise distros, and there were not any such complaints. So > most probably, we're fine. > Oh, I almost forgot about that one :) Indeed, 84209e87c696 was v6.2 and c8070b787519 was v6.5. ... and c8070b787519 was primarily concerned about !FOLL_LONGTERM usage, so that makes sense that they would still run into zeropages. For vfio, 84209e87c696 did the trick. -- Cheers, David / dhildenb