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[80.187.67.108]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c42bb49a4esm3560295a12.9.2024.09.17.03.28.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 17 Sep 2024 03:28:07 -0700 (PDT) Message-ID: Date: Tue, 17 Sep 2024 12:28:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2 3/7] mm: Use ptep_get() for accessing PTE entries To: Anshuman Khandual , linux-mm@kvack.org Cc: Andrew Morton , Ryan Roberts , "Mike Rapoport (IBM)" , Arnd Bergmann , x86@kernel.org, linux-m68k@lists.linux-m68k.org, linux-fsdevel@vger.kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org References: <20240917073117.1531207-1-anshuman.khandual@arm.com> <20240917073117.1531207-4-anshuman.khandual@arm.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: <20240917073117.1531207-4-anshuman.khandual@arm.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-Rspamd-Queue-Id: 382DE140012 X-Stat-Signature: wewe8p7kfn9jubreacop7mtu5cabwyxf X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1726568893-87629 X-HE-Meta: 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 UeJl2y4b 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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 17.09.24 09:31, Anshuman Khandual wrote: > Convert PTE accesses via ptep_get() helper that defaults as READ_ONCE() but > also provides the platform an opportunity to override when required. This > stores read page table entry value in a local variable which can be used in > multiple instances there after. This helps in avoiding multiple memory load > operations as well possible race conditions. > Please make it clearer in the subject+description that this really only involves set_pte_safe(). > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Ryan Roberts > Cc: "Mike Rapoport (IBM)" > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Anshuman Khandual > --- > include/linux/pgtable.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index 2a6a3cccfc36..547eeae8c43f 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -1060,7 +1060,8 @@ static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b) > */ > #define set_pte_safe(ptep, pte) \ > ({ \ > - WARN_ON_ONCE(pte_present(*ptep) && !pte_same(*ptep, pte)); \ > + pte_t __old = ptep_get(ptep); \ > + WARN_ON_ONCE(pte_present(__old) && !pte_same(__old, pte)); \ > set_pte(ptep, pte); \ > }) > I don't think this is necessary. PTE present cannot flip concurrently, that's the whole reason of the "safe" part after all. Can we just move these weird set_pte/pmd_safe() stuff to x86 init code and be done with it? Then it's also clear *where* it is getting used and for which reason. -- Cheers, David / dhildenb