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[2003:cb:c706:2000:e44c:bc46:d8d3:be5]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-439a0cc11c6sm30458885e9.16.2025.02.20.04.05.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Feb 2025 04:05:46 -0800 (PST) Message-ID: <66467b8d-9e8c-4a74-b932-9ddc3fcf459a@redhat.com> Date: Thu, 20 Feb 2025 13:05:45 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: Do not access pgmap for non zone device pages To: Balbir Singh , akpm@linux-foundation.org, linux-mm@kvack.org Cc: apopple@nvidia.com, Jason Gunthorpe , Dan Williams References: <20250219231337.364133-1-balbirs@nvidia.com> <329060a2-8871-4adf-9a45-f0afaedc8848@redhat.com> <22cff2d7-a9db-4a86-a168-d610fc00cdd9@nvidia.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: <22cff2d7-a9db-4a86-a168-d610fc00cdd9@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 51fnQtI6x70abC6iOFMJDSCmdxW1KGsgZ4oJwnRIekE_1740053148 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 0A05F40006 X-Stat-Signature: ro3d77c3zbmcx6xwgymw7hp51z7rmcxs X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1740053150-510668 X-HE-Meta: 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 2JsVm8bp 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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 20.02.25 12:58, Balbir Singh wrote: > On 2/20/25 22:48, David Hildenbrand wrote: >> On 20.02.25 00:13, Balbir Singh wrote: >>> page_pgmap() is referenced before checking if the page is a zone >>> device page and this triggers the warning in page_pgmap(). Refactor >>> the code to use the helper function after relevant checks. >>> >>> Cc: Alistair Popple >>> Cc: Jason Gunthorpe >>> Cc: David Hildenbrand >>> Cc: Dan Williams >>> >>> Signed-off-by: Balbir Singh >>> --- >>> >>> Fixes: 7f1cfd71153b ("mm: allow compound zone device pages") on >>> mm-unstable >> >> Is there actually something broken? At least for now, reading folio->pgmap should just work, although it might be garbage. >> > > It triggers the VM_WARN_ON_ONCE_PAGE > > static inline struct dev_pagemap *page_pgmap(const struct page *page) > { > VM_WARN_ON_ONCE_PAGE(!is_zone_device_page(page), page); > return page_folio(page)->pgmap; > } > > Nothing is broken, because the code below has checks for is_device_coherent_page(), > but in general I think the WARN_ON is correct because it warns us against garbage > and it's propagation if the correct checks are not in place. Ah! Now I read your "triggers the warning in page_pgmap()" in the description. It's usually a good idea to just include the splat you observed, if you did, and call it "triggers the VM_WARN_ON_ONCE_PAGE". The "Fixes:" should go above the "---" in that case. > > >>> >>>   mm/migrate_device.c | 13 ++++++++----- >>>   1 file changed, 8 insertions(+), 5 deletions(-) >>> >>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>> index 6771893d4601..e0bf771edb6f 100644 >>> --- a/mm/migrate_device.c >>> +++ b/mm/migrate_device.c >>> @@ -153,14 +153,17 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>                   goto next; >>>               } >>>               page = vm_normal_page(migrate->vma, addr, pte); >>> -            pgmap = page_pgmap(page); >>>               if (page && !is_zone_device_page(page) && >>>                   !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) >>>                   goto next; >>> -            else if (page && is_device_coherent_page(page) && >>> -                (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) || >>> -                 pgmap->owner != migrate->pgmap_owner)) >>> -                goto next; >>> +            else if (page && is_device_coherent_page(page)) { >>> +                pgmap = page_pgmap(page); >>> + >>> +                if (!(migrate->flags & >>> +                    MIGRATE_VMA_SELECT_DEVICE_COHERENT) || >>> +                    pgmap->owner != migrate->pgmap_owner) >>> +                    goto next; >>> +            } >> >> Coding style wants you to use >> >> if () { >> >> } else if { >> >> } >> >> Not >> >> if () >> else if { >> >> } >> > > Ack, checkpatch.pl missed it, but agreed > >> >> Something simpler might be >> >> page_pgmap(page)->owner != migrate->pgmap_owner >> > > Yep, I had that and dropped it, the four clauses made it feel that it might > benefit from a split. Right, the mixture of && and || is confusing. So with the {} Acked-by: David Hildenbrand Thanks! -- Cheers, David / dhildenb