From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AED8752CCFE; Wed, 14 Oct 2026 13:49:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791985755; cv=none; b=S4Mfq88MXvsOIwqoSLdFAjyfC9JKSsRd1hVXsY1R90aYbDYbs77VG5DL/G66ge0swKQsAxu5yv0tteauN9KGwvMYtHfuSlTQ/0qIeU5v5SpUkc9xPOGu6quhztOR2ur9L9wv3abfhdfJfkDqqmBfJZycotTbIS9hJqk9sRn/Mw8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791985755; c=relaxed/simple; bh=ATEv/LgDAtufUjFNthhjb/yPJrgbH8CUVruzjsRTs8c=; h=Message-ID:Date:MIME-Version:Subject:From:To:Cc:References: In-Reply-To:Content-Type; b=G1wqUN+HbnozRwrVg4QBsVfmYQMIKm5w6bYAM+n7EdAVmmg8sa6gVlugWcohRrMUqec2JlSuoEz+e+pUgRbqkke94WIk7lb7BdIVETA4bRzjcESO2wy6TFDG/leWc3+9NO2M4OvLEIU+am8pWUcFKt0WJAwVTImV9xgd0HxdpzY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PPzlrtN5; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PPzlrtN5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2F6631F00A2F; Wed, 14 Oct 2026 13:49:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791985753; bh=VlLY8lFnuENoZRIPsEzQ8Q4quedoDle8h5IdEqEOpQ8=; h=Date:Subject:From:To:Cc:References:In-Reply-To; b=PPzlrtN5VSLvNoSdjJv8S6IWz9JcAweG/P0+UvtQ1sFu3nTPMRHLcXiHWN6/+oOnh b6OtZ7RNPpBkN6oXyFeYTlWLq8AVTzH20JzehD7cT8uw2qqGkQVdsEU2Z2f5T7zxkC vTf251qwCUxZmP+wHqVHv04VZChr+GLxPVOZltV1asZdwZhTXbPgUqJMB2nd2dAvM+ aI/JIprBTd4sXSeuAB2rchOiIBEH2YxSdtlKkNWOhmY+ePYdJLniCVRNHZRbaaplMG +PBAufsc9gt/VUYrXHHRlIK1CL1g+vCrrpqELVc8ry9r2hSzKlV6OkbaT3ClmIlA7v tafO21tHnIPig== Message-ID: <807e8d2e-e7c1-4491-a3e1-21d84cc58946@kernel.org> Date: Wed, 14 Oct 2026 15:49:05 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: fix address wraparound when scanning large folio PTEs From: "David Hildenbrand (Arm)" To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Ying Huang , Baolin Wang , Barry Song , Ryan Roberts , Chuanhua Han , Kiryl Shutsemau , Kyle Zeng , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20261013-folio_pte_scan_range-v1-1-c50dc30bf6ad@kernel.org> <9add8400-66c1-47e9-b5af-7a4081ebf3c4@kernel.org> <06930044-4bcb-4478-8a6f-2dd3cf6d290e@kernel.org> 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: <06930044-4bcb-4478-8a6f-2dd3cf6d290e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/14/26 15:45, David Hildenbrand (Arm) wrote: > On 10/14/26 15:27, Lorenzo Stoakes (ARM) wrote: >> On Wed, Oct 14, 2026 at 10:12:06AM +0200, David Hildenbrand (Arm) wrote: >> >> Since I'm convinced the logic itself is correct: >> >> Reviewed-by: Lorenzo Stoakes (ARM) >> >> This cycle is brutal enough not to hold up fixes :>) >> >> >>> >>> I had that, but decided "not worth it for an internal helper". >>> >>> Is anything here really that confusing to understand in mm/memory.c context? I >>> highly doubt it. >> >> I mean I found it pretty confusing :) >> >> But this is a nice to have it's not a big deal. >> >>> >>> Ugly. >> >> Yup, fair enough. >> >>> >>> >>> I can just call it "folio_pte_range()". Slightly similar (but different) to >>> "folio_pte_batch()" >> >> OK that works. > > Ok, let's do that. > >>> >>> Yes. It's fairly common, though, to handle clamping of exclusive ends that way. >> >> Right, it took me a while to figure this out though. >> >> It involves an implicit assumption in there too, that _one_ of these values is >> known not to overflow. >> >>> >>> As replied elsewhere, I had that, but decided to open-code as pmd_addr_end() has >>> very weird semantics with folded page tables, where we just don't clamp at all. >> >> Hmm how so? >> >> The logic seems, at a glance, equivalent? > > It's the following thing that adds confusion: > > include/asm-generic/pgtable-nopmd.h:#define pmd_addr_end(addr, end) > (end) > > I think we have to assume here that with NOPMD we will never end up in this code > because large folios will not apply (each PMD table has exactly one entry as of > today, so we cannot map large folios .... I think). > > I can try condensing that in a comment and cross my fingers that that is the > case. I tried that now. and codex review already tells me: > > • [P1] Folded PMDs can reach this helper — memory.c:4948 (mm/memory.c:4948). > The comment’s assumption is false: arm64 with 64 KiB pages and 42-bit VA uses > folded PMDs and supports THP and > NUMA balancing. Here, pmd_addr_end() returns vma->vm_end without clamping. A > large folio remapped across a PTE-table boundary can therefore make > numa_rebuild_large_mapping() walk beyond > the mapped PTE table. The previous code explicitly limited this to pt_start > + PMD_SIZE. Cap the forward distance at PMD_SIZE - (addr & ~PMD_MASK) as well as > the VMA and folio limits. > > Let me see if there is any truth to that ... Ok, the PMD table as a single entry, but the PTE table obviously has 2k entries :) So large folios are possible and pmd_addr_end() would be wrong in this context. pmd_addr_end() really only works in page table walkers ... -- Cheers, David