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(p200300cbc7175f00c9496700cce1e60b.dip0.t-ipconnect.de. [2003:cb:c717:5f00:c949:6700:cce1:e60b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42100fb0905sm32266375e9.41.2024.05.23.12.03.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 May 2024 12:03:24 -0700 (PDT) Message-ID: Date: Thu, 23 May 2024 21:03:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/debug_vm_pgtable: Drop RANDOM_ORVALUE trick To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Andrew Morton , Pavel Tatashin , "Aneesh Kumar K . V" , Gavin Shan , Anshuman Khandual , Mikhail Gavrilov References: <20240523132139.289719-1-peterx@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: <20240523132139.289719-1-peterx@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: 7bit X-Stat-Signature: gdkqosthtgwnnfqhznu5xbnhxi1in131 X-Rspamd-Queue-Id: 421AF18000F X-Rspam-User: X-Rspamd-Server: rspam01 X-HE-Tag: 1716491008-320833 X-HE-Meta: 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 oN42VfHs 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 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 23.05.24 15:21, Peter Xu wrote: > Macro RANDOM_ORVALUE was used to make sure the pgtable entry will be > populated with !none data in clear tests. > > The RANDOM_ORVALUE tried to cover mostly all the bits in a pgtable entry, > even if there's no discussion on whether all the bits will be vaild. Both > S390 and PPC64 have their own masks to avoid touching some bits. Now it's > the turn for x86_64. > > The issue is there's a recent report from Mikhail Gavrilov showing that > this can cause a warning with the newly added pte set check in commit > 8430557fc5 on writable v.s. userfaultfd-wp bit, even though the check > itself was valid, the random pte is not. We can choose to mask more bits > out. > > However the need to have such random bits setup is questionable, as now > it's already guaranteed to be true on below: > > - For pte level, the pgtable entry will be installed with value from > pfn_pte(), where pfn points to a valid page. Hence the pte will be > !none already if populated with pfn_pte(). > > - For upper-than-pte level, the pgtable entry should contain a directory > entry always, which is also !none. > > All the cases look like good enough to test a pxx_clear() helper. Instead > of extending the bitmask, drop the "set random bits" trick completely. Add > some warning guards to make sure the entries will be !none before clear(). > > Cc: David Hildenbrand > Cc: Pavel Tatashin > Cc: Aneesh Kumar K.V > Cc: Gavin Shan > Cc: Anshuman Khandual > Reported-by: Mikhail Gavrilov > Tested-by: Mikhail Gavrilov > Link: https://lore.kernel.org/r/CABXGCsMB9A8-X+Np_Q+fWLURYL_0t3Y-MdoNabDM-Lzk58-DGA@mail.gmail.com > Signed-off-by: Peter Xu Acked-by: David Hildenbrand -- Cheers, David / dhildenb