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[2003:cb:c706:2700:abf9:4eac:588c:adab]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4405b4c8294sm45007165e9.2.2025.04.17.01.09.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Apr 2025 01:09:56 -0700 (PDT) Message-ID: Date: Thu, 17 Apr 2025 10:09:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/huge_memory: fix dereferencing invalid pmd migration entry From: David Hildenbrand To: Hugh Dickins Cc: Gavin Guo , linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, ziy@nvidia.com, linmiaohe@huawei.com, revest@google.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org References: <20250414072737.1698513-1-gavinguo@igalia.com> <27d13454-280f-4966-b694-d7e58d991547@redhat.com> <6787d0ea-a1b9-08cf-1f48-e361058eec20@google.com> <83f17b85-c9fa-43a0-bec1-22c8565b67ad@redhat.com> <98d1d195-7821-4627-b518-83103ade56c0@redhat.com> 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: <98d1d195-7821-4627-b518-83103ade56c0@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: --0ubfk55HZJvtzBIU8rNRaa8XHLbNXadkmkpaVftDk_1744877397 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: tudc5sowrqa34gz4gio6p1kqpsgn81p9 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 52778100003 X-Rspam-User: X-HE-Tag: 1744877400-159050 X-HE-Meta: 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 T4a3KydP 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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 17.04.25 10:07, David Hildenbrand wrote: > On 17.04.25 09:18, David Hildenbrand wrote: >> On 17.04.25 07:36, Hugh Dickins wrote: >>> On Wed, 16 Apr 2025, David Hildenbrand wrote: >>>> >>>> Why not something like >>>> >>>> struct folio *entry_folio; >>>> >>>> if (folio) { >>>> if (is_pmd_migration_entry(*pmd)) >>>> entry_folio = pfn_swap_entry_folio(pmd_to_swp_entry(*pmd))); >>>> else >>>> entry_folio = pmd_folio(*pmd)); >>>> >>>> if (folio != entry_folio) >>>> return; >>>> } >>> >>> My own preference is to not add unnecessary code: >>> if folio and pmd_migration entry, we're not interested in entry_folio. >>> But yes it could be written in lots of other ways. >> >> While I don't disagree about "not adding unnecessary code" in general, >> in this particular case just looking the folio up properly might be the >> better alternative to reasoning about locking rules with conditional >> input parameters :) >> > > FWIW, I was wondering if we can rework that code, letting the caller to the > checking and getting rid of the folio parameter. Something like this (incomplete, just to > discuss if we could move the TTU_SPLIT_HUGE_PMD handling). > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2a47682d1ab77..754aa3103e8bf 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3075,22 +3075,11 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, > pmd_t *pmd, bool freeze, struct folio *folio) > { > - VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio)); > VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); > - VM_WARN_ON_ONCE(folio && !folio_test_locked(folio)); > - VM_BUG_ON(freeze && !folio); > > - /* > - * When the caller requests to set up a migration entry, we > - * require a folio to check the PMD against. Otherwise, there > - * is a risk of replacing the wrong folio. > - */ > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || > - is_pmd_migration_entry(*pmd)) { > - if (folio && folio != pmd_folio(*pmd)) > - return; > + is_pmd_migration_entry(*pmd)) > __split_huge_pmd_locked(vma, pmd, address, freeze); > - } > } > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > diff --git a/mm/rmap.c b/mm/rmap.c > index 67bb273dfb80d..bf0320b03d615 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -2291,13 +2291,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > if (flags & TTU_SYNC) > pvmw.flags = PVMW_SYNC; > > - /* > - * unmap_page() in mm/huge_memory.c is the only user of migration with > - * TTU_SPLIT_HUGE_PMD and it wants to freeze. > - */ > - if (flags & TTU_SPLIT_HUGE_PMD) > - split_huge_pmd_address(vma, address, true, folio); > - > /* > * For THP, we have to assume the worse case ie pmd for invalidation. > * For hugetlb, it could be much worse if we need to do pud > @@ -2326,6 +2319,14 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > /* PMD-mapped THP migration entry */ > if (!pvmw.pte) { > + if (flags & TTU_SPLIT_HUGE_PMD) { > + split_huge_pmd_locked(vma, pmvw.address, pvmw.pmd, > + true, NULL); > + ret = false; > + page_vma_mapped_walk_done(&pvmw); > + break; > + } > + > subpage = folio_page(folio, > pmd_pfn(*pvmw.pmd) - folio_pfn(folio)); > VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || > > Likely, we'd have to adjust the CONFIG_ARCH_ENABLE_THP_MIGRATION coverage here, for TTU_SPLIT_HUGE_PMD to get handled even without that. Just an idea. -- Cheers, David / dhildenb