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[2003:cb:c708:5400:6c12:d0e2:3757:2963]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-374c602bd97sm11827328f8f.20.2024.09.05.01.15.31 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Sep 2024 01:15:31 -0700 (PDT) Message-ID: Date: Thu, 5 Sep 2024 10:15:30 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: arm64: document why pte is not advanced in contpte_ptep_set_access_flags() To: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Cc: ardb@kernel.org, catalin.marinas@arm.com, jhubbard@nvidia.com, mark.rutland@arm.com, v-songbaohua@oppo.com, will@kernel.org, Ryan Roberts References: <20240905081124.9576-1-21cnbao@gmail.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: <20240905081124.9576-1-21cnbao@gmail.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-Rspam-User: X-Rspamd-Queue-Id: 6CD4640014 X-Rspamd-Server: rspam01 X-Stat-Signature: b4z89qqhh53umkp7tpmicw6c3cki71o9 X-HE-Tag: 1725524138-549435 X-HE-Meta: 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 0ffcu8PS 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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 05.09.24 10:11, Barry Song wrote: > From: Barry Song > > According to David and Ryan, there isn't a bug here, even though we > don't advance the PTE entry, because __ptep_set_access_flags() only > uses the access flags from the entry. > > However, we always check pte_same(pte, entry) using the first entry > in __ptep_set_access_flags(). This means that the checks from 1 to > nr - 1 are not comparing the same PTE indexes (thus, they always > return false), which can be a bit confusing. To clarify the code, let's > add some comments. > > Reviewed-by: Ryan Roberts > Signed-off-by: Barry Song > Cc: Ard Biesheuvel > Cc: John Hubbard > Cc: Mark Rutland > Cc: Catalin Marinas > Cc: David Hildenbrand > Cc: Will Deacon > --- > -v2: > * collect Ryan's rb, thanks! > * doc why but not advance entry > * refine changelog and subject > > -v1: > https://lore.kernel.org/linux-mm/20240831083537.62111-1-21cnbao@gmail.com/ > > arch/arm64/mm/contpte.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c > index a3edced29ac1..55107d27d3f8 100644 > --- a/arch/arm64/mm/contpte.c > +++ b/arch/arm64/mm/contpte.c > @@ -421,6 +421,12 @@ int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > ptep = contpte_align_down(ptep); > start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > > + /* > + * We are not advancing entry because __ptep_set_access_flags() > + * only consumes access flags from entry. And since we have checked > + * for the whole contpte block and returned early, pte_same() > + * within __ptep_set_access_flags() is likely false. > + */ > for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) > __ptep_set_access_flags(vma, addr, ptep, entry, 0); > Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb