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b=EOKldVbvIfdnaD+P7TdPswSLRN+O9HifxN6uWB8N8hdEVWGAf8uN3yVuRNuqRgRfe o81M2I5yAgWGhNB0EmRa1Isd2tZlGCfIFBKvn7Qw2sb3+emXasJS53nw3LwsJdAXEo W1Sbi5NBo8+rHcsbn39WHpiBv1Fhj6ig+C911jyaEgdEstRAPNcKythrdY5GoKmKHz BNndFan+L1ioUCt6RaHPT9JrrLZQPtm1Lv3TJ/t1dsj+fI1Y2af7/27oWKBYhpQZst p1MqjL3tU+iVijQvuSWMbtSiVvfO8G7TAI5EZ2TK8Izeip3tCPQz3pPsHHI7ryX8Qw 0uRbih7+b2gfQ== Message-ID: Date: Fri, 17 Jul 2026 15:53:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/4] mm: introduce __ptent sparse attribute To: Alexander Gordeev , Kevin Brodsky , Chris Li , Gerald Schaefer , Heiko Carstens , Christian Borntraeger , Claudio Imbrenda Cc: linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org, Muhammad Usama Anjum References: 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D1D3F40004 X-Stat-Signature: fs7ucatiwxm6d3s8ytbmnc8rse6iwozc X-HE-Tag: 1784299997-216833 X-HE-Meta: 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 oGwIgNP9 HPWiu0wo/I8UOqGJTHqW2z7MYXnw21h9Rz+WcZdQwh0Jb02tWwvmFyilTmgh8puBONS/8gEqSsIuaYeiX1Fjtlg60mMGxTD35jYLzwzpG9JGRgPsJAoIB2POwNLaenGeU/2IJjk050RbnehBhPuV4dSCS3QiyERpK0b7ctY+i/STR2khJ8T0VDLLGpfqF1JLLApC/cUA3DPRE8AqBtK4ajsUYzlNhDBXY65pV48XO0uLDSv/J4u8AU9Iax4Vo0nknXvS66gw+8I5tHmGxU7KxNJErq2odsRZAcYgK6JmhxfPeMFs9BirtNcCCfFBd+GwaX+sYiIcaE9OvBEM4DHLRqJtDUFcJo7khPgmjbNT9fRH0Ebx9veUnmpcc2+f2xbaHfV2ubuSGa0Q0Uu0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/17/26 14:32, Alexander Gordeev wrote: > Hi All! > > This RFC is a result the implementation of lazy MMU mode on s390 [1]. > > Heiko Carstens requested some mechanism that would rule out direct > dereferencing of PTE pointers, which otherwise would bypass the per- > cpu cache on s390 and lead to catastrophic results. > > This is an attempt to introduce __ptent sparse attribute similar to > __private, but to be applied only to pte_t type by architectures. > When used with C=1 the modified sparse "dereference of PTE pointer" > warning is emitted. > > With using that new mechanism I was able to identify direct PTE > pointer dereferences, which should not have existed after commit > c33c794828f2 ("mm: ptep_get() conversion") (and its follow-ups). > > In addition to ptep_get() and set_pte() accessors I suggest to > introduce ptep_get_nopgtable() and set_pte_nopgtable() variants > to use when a PTE pointer does not point to the page table, but > rather to a copy of the PTE. These would allow dropping unnecessary > checks on s390, but is already the case for folio_pte_batch_flags(). > > Patches 1,2 are independent from the sparse rework and are good to go AFAICT. > Patch 3 is the required change to be coupled with the sparse rework below. > Patch 4 is an example of how __ptent was implemented on s390. > > I hesitate to post the sparse patch itself before the rework is is agreed, > but I am CC-ing the sparse mailing list. Usama is working on something bigger, whereby we introduce the concept of pte_t and hw_pte_t in common code, and allow to decouple them on architectures that really need (IOW that implement it in their arch code). On architecture that decouple both types, the compiler will do the type checking for us. The prototype patches I saw looked pretty encouraging (at least for pte_t, pmd_t is more involved). There is some information here: https://lore.kernel.org/r/6110202c-057b-4701-8c04-1a76ee7bb9ab@arm.com And I'm sure Usama can share some more details with you to give you a better idea if that would solve the problem for s390x as well. -- Cheers, David