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[2003:cb:c707:7600:5c18:5a7d:c5b7:e7a9]) by smtp.gmail.com with ESMTPSA id t9-20020adfeb89000000b0033dbeb2eb4dsm10297686wrn.110.2024.02.26.23.30.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 26 Feb 2024 23:30:40 -0800 (PST) Message-ID: <90471b2f-826e-4275-a9a3-ec673c3e6af8@redhat.com> Date: Tue, 27 Feb 2024 08:30:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm/memory: Fix boundary check for next PFN in folio_pte_batch() To: Lance Yang , akpm@linux-foundation.org Cc: ryan.roberts@arm.com, 21cnbao@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240227070418.62292-1-ioworker0@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: <20240227070418.62292-1-ioworker0@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-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: F337380003 X-Stat-Signature: 57nyqz9qs7gebjhixdd7nwasodn1zjbn X-Rspam-User: X-HE-Tag: 1709019044-394551 X-HE-Meta: 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 e2OrG1p4 i9+i8ZRkYGRFU3yVZ5nBegc7bUZHc3P/kbzhObL/xEgaBW3oGh2VJmkAUB2rlFQT1oQF1QpHoB1s0SLUoCUcaRKIY1ESlv2SPTsjmzb1WEmqw/t7VuoJdUkMaOggg6hCeQ7SRURdXfZmzFy/Ey3R95bDOpmmExUyawDjJ6ab50VvSbyV9KyUe3Pxyn/DfuW2i8vef0IBI0kGHyfo8FZcR+KuBRlqjO3p7M6BSSt0AEOlkiTTHrZug2mDooXrEg6rR9xWh9EN0hcDu8L9mjpcHy4ij4MUkPof7OxZN7aJ8GxDnbpp6eFY137LiNs+5A0dBNte2PlQ/ELwEskRpvU8I5PQNQ2+QaiHvxrQedn2Qf5dDrVMN7z2sWGK1MwafErp814lCbI3CXabqUPHMgpN+ua3iXM43m52/DXcJo4auKMKC28C94AjngTbGkbLMsyFB4Usq6DnPObZKla1TJNej08rfTxbxuIF7hLP/RFBs+fqO7nU= 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 27.02.24 08:04, Lance Yang wrote: > Previously, in folio_pte_batch(), only the upper boundary of the > folio was checked using '>=' for comparison. This led to > incorrect behavior when the next PFN exceeded the lower boundary > of the folio, especially in corner cases where the next PFN might > fall into a different folio. Which commit does this fix? The introducing commit (f8d937761d65c87e9987b88ea7beb7bddc333a0e) is already in mm-stable, so we would need a Fixes: tag. Unless, Ryan's changes introduced a problem. BUT I don't see what is broken. :) Can you please give an example/reproducer? We know that the first PTE maps the folio. By incrementing the PFN using pte_next_pfn/pte_advance_pfn, we cannot suddenly get a lower PFN. So how would pte_advance_pfn(folio_start_pfn + X) suddenly give us a PFN lower than folio_start_pfn? Note that we are not really concerned about any kind of pte_advance_pfn() overflow that could generate PFN=0. I convinces myself that that that is something we don't have to worry about. [I also thought about getting rid of the pte_pfn(pte) >= folio_end_pfn and instead limiting end_ptep. But that requires more work before the loop and feels more like a micro-optimization.] > > Signed-off-by: Lance Yang > --- > mm/memory.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 642b4f2be523..e5291d1e8c37 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -986,12 +986,15 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > pte_t *start_ptep, pte_t pte, int max_nr, fpb_t flags, > bool *any_writable) > { > - unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio); > + unsigned long folio_start_pfn, folio_end_pfn; > const pte_t *end_ptep = start_ptep + max_nr; > pte_t expected_pte, *ptep; > bool writable; > int nr; > > + folio_start_pfn = folio_pfn(folio); > + folio_end_pfn = folio_start_pfn + folio_nr_pages(folio); > + > if (any_writable) > *any_writable = false; > > @@ -1015,7 +1018,7 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > * corner cases the next PFN might fall into a different > * folio. > */ > - if (pte_pfn(pte) >= folio_end_pfn) > + if (pte_pfn(pte) >= folio_end_pfn || pte_pfn(pte) < folio_start_pfn) > break; > > if (any_writable) -- Cheers, David / dhildenb