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b=IxxpSCtmgQ8r5uOHX3CS8mUlg7Q4a37vM06e/YT73FKCBbUmrQu+4Vj/89P5SYFKT R5MpM/cwzv9st9kD7vQxzKltEVryMB8H/9LpXQfafBSP2XiUskoWF/R4CFti4AA8cZ 1aNVhMQ2MhbL+Wp1OX5WO1wOAZ/oaxCX4ybz7G/QMEiIlYp4GJvFMSl2wh24uQyfm9 DqIrGGbdLU7k7AbJOcqxjDz01xd7cPHIWo2aPHmLyobKp/mYulTNaKeARvgFb0Q8Gl 6AN9PeobwjlTiEPvZA6wguXZgEUQHoPjKGBA1ba4cjyRlBufdLwuPVrZSkOnnosdyj XDH+iEPWyU04g== Message-ID: Date: Mon, 20 Apr 2026 21:29:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/2] mm/gup: add lockless access semantics on entries validation To: Alexander Gordeev , Kevin Brodsky , Ryan Roberts , Andrew Morton Cc: linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Heiko Carstens , Vasily Gorbik References: <55c295e17221dc882e09b4caddc7b3bf4f1309ba.1776684344.git.agordeev@linux.ibm.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: <55c295e17221dc882e09b4caddc7b3bf4f1309ba.1776684344.git.agordeev@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 84AB41C000A X-Rspamd-Server: rspam07 X-Stat-Signature: c5dd4e7d4h5hpg66y14rsy8uk7oz16sn X-Rspam-User: X-HE-Tag: 1776713390-218423 X-HE-Meta: U2FsdGVkX195MfNwQruxg5LgNSMIxDK5yNyRDmSIzPtqhSCV1C0qXVfzcFGC8vV00vetYEwnFL8xPu5SQZkc0tfARXiY0Eozv1FOZc/ThIzWRUZd4d8tmfDHFw02qkDKl5g4aeq53zOHO6tcZ2x7tasbH1Syzcya8MdlFyYCtOL0++DeYCx8X5jN7AcayfY+zbtmBYlmvZXVONeUABH05BJY3QBzXBJLP+GCRBt/7UOdRJMQkCAjOdmB6lTeRi5ezE9oMRQPqhEW5XVhvnjbZA6cwUW9RHYAai06IvTjlO2dA/GRLPA0ICvRw+L3KfArCmovPC4P1GslgeWKI4APFHlCEa4Y2Vt7zhlApZw8eWFdigRpPZJkCBDebSoeKx1jU/ZRAz4rhv7v8o8qxRo/TqspttsRBEgr5e2I92ARhmm1FHB571KFgblm9KLJcv7iG8cB10t5JN9HcWGvgx6hezCzp+JJdb4egMj2AxnTFwWQXgCNHesDAJz8Lz89UVSYzWdNguS3ZVXKhHqiRtnWJDKd5qAVknSJPqSijX5Otymz3tC40t3fdGsJho9pR97q8MTl7CjLojy0KqOaDXpU+9E6PixwtorDiJiU7iBI9+T1tXLyocoi/FWVumcxwwULxAE5iJGYFLFiStytfTY8UD6C1Fw1KtWCTng/6SNRqmwlRsSi0+tIqkeG3Fi+CV61CMKVmajdqrgbwsOWadpbH8mKmU15j1lFq8Vlyu+j+MgSDHLIgPuKTlVZYYo/SVL3aU3zr/djTU+oxf9ejGVXQ7ASa32u9uy63257gsJR/2pIEi38DgHiywADnxQJ+PyLuxdO45nLqzTmgv6V9i8lEq4ViflOqvtuzhZPOnSprJlVjfiB3SwTYk3Mu72D6MY1l+9YA3u5890KCqQPeVbp02Av9QG53ymgqPW9kAsW+6Ak8Og8Co9h2Mw9tmlyBvdPViS1IM/X4u6LGpmGmCX cl1F+LNj YgUKBtz11rWG8ekKLdPljzxzpAXBzvTCPMNr2xf5ybvB9bU2IQ/jjhKa5+b+PYiWc8T8HZKEkBEuvzu11T213mNnHVyYs6u41GeEzsfnr4wSUxK/vzcg0z9a0DOyqnhbyafeWN4uerrMwy/LrCoA7g2phNnJ7FWGvwUISASumfkpPN6A1C4deMDMrELGt9ceBIQumm8oyDPGLS77KfyihY6bKo15xWd1A6Qy+04EghOrFzwbmbhYhlhM3pA/OsCs9jSPYZ3oNdUrIAN3M3WJBm1v9fw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/20/26 14:13, Alexander Gordeev wrote: > The PTE validation in gup_fast_pte_range() is inconsistent with the > prior value acquisition in the sense that it drops the lockless > access semantics. > > Although this is highly unlikely, prevent a future scenario in which > a semantically mismatching ptep_get() incorrectly yields the same > result as the preceding ptep_get_lockless(), while ptep_get_lockless() > would otherwise return a different value. > > Likewise the PMD validation is inconsistent with the prior value > acquisition in gup_fast_pmd_range(). > > Signed-off-by: Alexander Gordeev > --- > mm/gup.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index d149a4b0df71..236450feea9a 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2865,8 +2865,8 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, > if (!folio) > goto pte_unmap; > > - if (unlikely(pmd_val(pmd) != pmd_val(pmdp_get(pmdp))) || > - unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) { > + if (unlikely(pmd_val(pmd) != pmd_val(pmdp_get_lockless(pmdp))) || > + unlikely(pte_val(pte) != pte_val(ptep_get_lockless(ptep)))) { > gup_put_folio(folio, 1, flags); > goto pte_unmap; > } > @@ -2942,7 +2942,7 @@ static int gup_fast_pmd_leaf(pmd_t orig, pmd_t *pmdp, unsigned long addr, > if (!folio) > return 0; > > - if (unlikely(pmd_val(orig) != pmd_val(pmdp_get(pmdp)))) { > + if (unlikely(pmd_val(orig) != pmd_val(pmdp_get_lockless(pmdp)))) { > gup_put_folio(folio, refs, flags); > return 0; > } Oh, that should be squashed into #1 :) -- Cheers, David