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t=1791970899; bh=eknjK7272CVNf6tS/VepL4H992+z6bNQqkyA1iFz+tQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=T5d8KMHdYrwyQOI2inOJa8WADx/WcYcVUhf6HVnoAs+XC9nXjkZm2J+GXmVN4C+jc MgD2TefOp8QXb1QXs11PcxQ7lerPEtPipacMohaLtsKHaicZ816//O0j1J2BqrJ7u0 sxvKsEnURNR0O3v1wZBuIrFfB+QxxR5C10+SqUwVEIsjX9etaC53NgnlBkohUuSFhF hAjUjxgM0DPiESCpMHF/2ONQp5IEVQfNDcFpnLi6DrnnttnyW0blAnb/eLM2H5EXed YGCBBmRzuqZcs7uFBQLBFsEQkUTNGcAHsgGQEGqTpK5Td6GAtZ7CxI6orrb7JvXAoU 3apxqry9108sA== Message-ID: Date: Wed, 14 Oct 2026 11:41:32 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64/mm: restrict transparent contpte mappings to valid PTEs To: Zhao Gongyi , catalin.marinas@arm.com, will@kernel.org, Ryan Roberts Cc: ryan.roberts@arm.com, dev.jain@arm.com, baolin.wang@linux.alibaba.com, lance.yang@linux.dev, mark.rutland@arm.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261013093600.54995-1-zhaogongyi@bytedance.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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 B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20261013093600.54995-1-zhaogongyi@bytedance.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: 31wh1r4yxcdc5fwrkbwnuabrsnfuwd9r X-Rspamd-Queue-Id: 59163160005 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1791970900-207733 X-HE-Meta: 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 qsiM3Fe5 KCatdVzgn6L8ong7X1U++7UH05LiDuYSdL5hY/Sdv2M9cucxJ/yxmUYp8FYb/jfeJ7d7hLd40rEqP1XJGfLI1BIZCi8I7WgWM85bZ9wSw0hzV1SFwZNZgqyR2a9eI57/LDy6hK2LEeQEfhB4GIzZzDPh4y+SfvyPNxnhurSlv0vfloHbsUfDbj3snP5qjqvbjjUGhj7Vp3jTOABUM7t+a4GzJ1XJaXVMVdvlM3x+yfLpPMj6WlEOA3gIVitDMMSXFGrYRxRgV798HbuWDf6XiezP366xs5lcEyjYsYtOUaDYXMDFBU1wt0mhuxUM3/2KIbgH6+ls38RsT+MAwpcxqEJQe/nWWuHWoFj3QEZblFV4hYYRgScPZi0v9kUWdq51zmQyh Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: CCing Ryan: https://lore.kernel.org/r/20261013093600.54995-1-zhaogongyi@bytedance.com On 10/13/26 11:36, Zhao Gongyi wrote: > The transparent contpte layer treats PTE_CONT as software state: when a > PTE has PTE_CONT set, the contpte helpers may align the operation to a > CONT_PTE_SIZE block and operate on the whole block. That invariant only > makes sense for valid mappings. Explicit users such as hugetlb manage > their contiguous encodings separately. > > contpte_set_ptes() currently sets PTE_CONT from alignment alone. Batched > set_ptes() users can therefore install present-invalid PTEs with > PTE_CONT set, for example mprotect(PROT_NONE), NUMA hinting through > modify_prot_commit_ptes(), fork() copying a PROT_NONE large folio, or a > PMD split installing PAGE_NONE PTEs. > > This is not a hardware programming problem: invalid descriptors are not > translated, so the hardware ignores descriptor bits such as PTE_CONT. It > is a software-state problem. Some arm64 fast paths intentionally test > pte_cont() directly instead of pte_valid_cont(), for example commit > 9970a9a27ffc ("arm64: mm: implement the architecture-specific > test_and_clear_young_ptes()"). Fixing the producer side preserves these > fast paths and covers all consumers. > > In the observed failure, mprotect(PROT_NONE) installed a full > CONT_PTE_SIZE range of present-invalid PTEs with PTE_CONT set. > MADV_GUARD_INSTALL then zapped one PTE. The nr == 1 clear_full_ptes() > path only unfolds pte_valid_cont() entries, so the neighbouring > present-invalid entries kept PTE_CONT while the target entry became a > guard marker. Hm, is there a good reason why we cannot just use the cont-pte bit for all *present* PTEs, even if HW would not be prepared to benefit (!pte_valid())? I guess we really only have to make sure to shatter properly, right? -- Cheers, David