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[2003:cb:c741:c700:3db9:94c9:28b0:34f2]) by smtp.gmail.com with ESMTPSA id o3-20020a5d62c3000000b0033ec94c6277sm12096327wrv.115.2024.03.26.06.11.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Mar 2024 06:11:57 -0700 (PDT) Message-ID: <15117d1a-a03b-4ad5-9900-4c968212137f@redhat.com> Date: Tue, 26 Mar 2024 14:11:56 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/3] selftests/memfd_secret: add vmsplice() test From: David Hildenbrand To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Miklos Szeredi , Lorenzo Stoakes , xingwei lee , yue sun References: <20240325134114.257544-1-david@redhat.com> <20240325134114.257544-3-david@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: 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: 7bit X-Rspamd-Queue-Id: 3D1C64001A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: bhdqjsgfxkfukseratnjg7mjebcymsif X-HE-Tag: 1711458722-438465 X-HE-Meta: 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 FEX090Kq Bo0fDit0tjAdIW03TCFL56agtaiWfd0vvl+JgTjjqjc026Xz4ma0Lct7+A3d4P2lHrzc47C9Pwux01KauzjIsAObgggZs8pq97uoW4buJpMVdeZkCB1xObgaibTrgFbRrDw4sdKtPyvvaa7xUf1uK3O4WEW/96E1D62DiJYUOf0HrrfRCRRRppC0Wcqzpm/fo2zRLK526QMY+Kmh17J+t9Z5vWQ== 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 26.03.24 13:32, David Hildenbrand wrote: > On 26.03.24 07:17, Mike Rapoport wrote: >> Hi David, >> >> On Mon, Mar 25, 2024 at 02:41:13PM +0100, David Hildenbrand wrote: >>> Let's add a simple reproducer for a scneario where GUP-fast could succeed >>> on secretmem folios, making vmsplice() succeed instead of failing. The >>> reproducer is based on a reproducer [1] by Miklos Szeredi. >>> >>> Perform the ftruncate() only once, and check the return value. >>> >>> For some reason, vmsplice() reliably fails (making the test succeed) when >>> we move the test_vmsplice() call after test_process_vm_read() / >>> test_ptrace(). >> >> That's because ftruncate() call was in test_remote_access() and you need it >> to mmap secretmem. > > I don't think that's the reason. I reshuffled the code a couple of times > without luck. > > And in fact, even executing the vmsplice() test twice results in the > second iteration succeeding on an old kernel (6.7.4-200.fc39.x86_64). > > ok 1 mlock limit is respected > ok 2 file IO is blocked as expected > not ok 3 vmsplice is blocked as expected > ok 4 vmsplice is blocked as expected > ok 5 process_vm_read is blocked as expected > ok 6 ptrace is blocked as expected > > Note that the mmap()+memset() succeeded. So the secretmem pages should be in the page table. > > > Even weirder, if I simply mmap()+memset()+munmap() secretmem *once*, the test passes > > diff --git a/tools/testing/selftests/mm/memfd_secret.c b/tools/testing/selftests/mm/memfd_secret.c > index 0acbdcf8230e..7a973ec6ac8f 100644 > --- a/tools/testing/selftests/mm/memfd_secret.c > +++ b/tools/testing/selftests/mm/memfd_secret.c > @@ -96,6 +96,14 @@ static void test_vmsplice(int fd) > return; > } > > + mem = mmap(NULL, page_size, prot, mode, fd, 0); > + if (mem == MAP_FAILED) { > + fail("Unable to mmap secret memory\n"); > + goto close_pipe; > + } > + memset(mem, PATTERN, page_size); > + munmap(mem, page_size); > + > mem = mmap(NULL, page_size, prot, mode, fd, 0); > if (mem == MAP_FAILED) { > fail("Unable to mmap secret memory\n"); > > ok 1 mlock limit is respected > ok 2 file IO is blocked as expected > ok 3 vmsplice is blocked as expected > ok 4 process_vm_read is blocked as expected > ok 5 ptrace is blocked as expected > > > ... could it be that munmap()+mmap() will end up turning these pages into LRU pages? Okay, now I am completely confused. secretmem_fault() calls filemap_add_folio(), which should turn this into an LRU page. So secretmem pages should always be LRU pages. .. unless we're batching in the LRU cache and haven't done the lru_add_drain() ... And likely, the munmap() will drain the lru cache and turn the page into an LRU page. Okay, I'll go make sure if that's the case. If so, relying on the page being LRU vs. not LRU in GUP-fast is unreliable and shall be dropped. -- Cheers, David / dhildenb