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[2003:cb:c708:e100:4f41:ff29:a59f:8c7a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e4c1f2esm5266467f8f.98.2025.01.10.11.17.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 10 Jan 2025 11:17:04 -0800 (PST) Message-ID: <25e02685-4f1d-47fa-be5b-01ff85bb0ce2@redhat.com> Date: Fri, 10 Jan 2025 20:17:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mm-unstable v1] mm/hugetlb_vmemmap: fix memory loads ordering From: David Hildenbrand To: Matthew Wilcox Cc: Yu Zhao , Andrew Morton , Mateusz Guzik , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Will Deacon References: <20250107043505.351925-1-yuzhao@google.com> <85ea0bc9-0892-489d-b42b-430ff8a1f368@redhat.com> <559ea5ca-fea2-4a0a-a099-23e2d972f6e6@redhat.com> <57447786-9184-427b-b5de-321784e946f5@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/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: <57447786-9184-427b-b5de-321784e946f5@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 1eA1v6Oi9XB3uqUhtVx3fq_5a5pgdRr3ZJ-TJWvm2hQ_1736536626 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: zwaajxrhcoxi46pkty58myaqpueqaup3 X-Rspamd-Queue-Id: BB3A64000B X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1736536630-831129 X-HE-Meta: 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 ZtfM2gWL NDFIhdJ76f+a6qMibW2kCiDbrEtmNeVUGh+LuDQeVwtJKzDu5ttwXOuBDA22vnTwrZhEqMAz21VVfZJnKCOLZHbvC7wO+j3cX6MTK3p7OmWv+X/WoM/+/+54wtsbB1FZyjWvMv7ZsUVQTAs+fMkXKlgJc7HQn/2W9zLY3CxgUsevCW7k428ltpW4UqKR96gD7BTfa7rF4oJZXS5H/cn2c3NzzPdKhbmx+xWZKHvRfVu9uftHQ5dmShPL8t5cwDbRY4gHZyPHxOsDShKnr6gSGFbSD9xiBkGUO8U6tdXcStbr6ObR24MjS2aZ5HaNNs8enNCWb8mGEzXoWVmtfu0v/IUVb7puaduIkm3i9IiLdU2+5c4rCHu5G26v7fcrkVBZ2mGo1a9OwsUsRbOeniyaNE+vgUaVfercrZwL+xFK5fm1jRwSfYwEd2HilidLI4AAAv1SO 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 10.01.25 20:04, David Hildenbrand wrote: > On 07.01.25 18:02, David Hildenbrand wrote: >> On 07.01.25 17:35, Matthew Wilcox wrote: >>> On Tue, Jan 07, 2025 at 09:49:18AM +0100, David Hildenbrand wrote: >>>>> +++ b/include/linux/page-flags.h >>>>> @@ -212,7 +212,7 @@ static __always_inline const struct page *page_fixed_fake_head(const struct page >>>>> * cold cacheline in some cases. >>>>> */ >>>>> if (IS_ALIGNED((unsigned long)page, PAGE_SIZE) && >>>>> - test_bit(PG_head, &page->flags)) { >>>>> + test_bit_acquire(PG_head, &page->flags)) { >>>> >>>> This change will affect all page_fixed_fake_head() users, like ordinary >>>> PageTail even on !hugetlb. >>> >>> I've been looking at the callers of PageTail() because it's going to >>> be a bit of a weird thing to be checking in the separate-page-and-folio >>> world. Obviously we can implement it, but there's a bit of a "But why >>> would you want to ask that question" question. >>> >>> Most current occurrences of PageTail() are in assertions of one form or >>> another. Fair enough, not performance critical. >>> >>> make_device_exclusive_range() is a little weird; looks like it's trying >>> to make sure that each folio is only made exclusive once, and ignore any >>> partial folios which overlap the start of the area. >> >> I could have sworn we only support small folios here, but looks like >> we do support large folios. >> >> IIUC, there is no way to identify reliably "this folio is device exclusive", >> the only hint is "no mappings". The following might do: >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index c6c4d4ea29a7e..1424d0a351a86 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -2543,7 +2543,13 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start, >> >> for (i = 0; i < npages; i++, start += PAGE_SIZE) { >> struct folio *folio = page_folio(pages[i]); >> - if (PageTail(pages[i]) || !folio_trylock(folio)) { >> + >> + /* >> + * If there are no mappings, either the folio is actually >> + * unmapped or only device-exclusive swap entries point at >> + * this folio. >> + */ >> + if (!folio_mapped(folio) || !folio_trylock(folio)) { >> folio_put(folio); >> pages[i] = NULL; >> continue; > > I stared longer at this, and not sure if that will work. > > The PageTail() is in place because we return with the folio locked on > success, so we won't trylock again on tail pages. > > But staring at page_make_device_exclusive_one(), I am not sure if it > does what we want in all cases ... > > ... and the hmm selftests just keeps failing upstream as well?! huh. :) > > I'll try spending some time on this to see if I can grasp what needs to > be done and how it could be handled ... better. > As expected ... # echo never > /sys/kernel/mm/transparent_hugepage/enabled # ./hmm-tests ... # RUN hmm.hmm_device_private.exclusive ... # OK hmm.hmm_device_private.exclusive ok 21 hmm.hmm_device_private.exclusive # RUN hmm.hmm_device_private.exclusive_mprotect ... # OK hmm.hmm_device_private.exclusive_mprotect ok 22 hmm.hmm_device_private.exclusive_mprotect # RUN hmm.hmm_device_private.exclusive_cow ... # OK hmm.hmm_device_private.exclusive_cow ok 23 hmm.hmm_device_private.exclusive_cow # RUN hmm.hmm_device_private.hmm_gup_test ... # OK hmm.hmm_device_private.hmm_gup_test ... # echo always > /sys/kernel/mm/transparent_hugepage/enabled ... # RUN hmm.hmm_device_private.exclusive ... # hmm-tests.c:1751:exclusive:Expected ret (-16) == 0 (0) # exclusive: Test terminated by assertion # FAIL hmm.hmm_device_private.exclusive not ok 21 hmm.hmm_device_private.exclusive # RUN hmm.hmm_device_private.exclusive_mprotect ... # hmm-tests.c:1805:exclusive_mprotect:Expected ret (-16) == 0 (0) # exclusive_mprotect: Test terminated by assertion # FAIL hmm.hmm_device_private.exclusive_mprotect not ok 22 hmm.hmm_device_private.exclusive_mprotect # RUN hmm.hmm_device_private.exclusive_cow ... # hmm-tests.c:1858:exclusive_cow:Expected ret (-16) == 0 (0) # exclusive_cow: Test terminated by assertion # FAIL hmm.hmm_device_private.exclusive_cow not ok 23 hmm.hmm_device_private.exclusive_cow So rejecting folio_test_large() would likely achieve the same thing right now. -- Cheers, David / dhildenb