From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 929DDCC6B1D for ; Wed, 14 Oct 2026 13:49:18 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7BF4C6B0095; Wed, 14 Oct 2026 09:49:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 796426B0096; Wed, 14 Oct 2026 09:49:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6AD786B0098; Wed, 14 Oct 2026 09:49:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 4CB746B0095 for ; Wed, 14 Oct 2026 09:49:17 -0400 (EDT) Received: from smtpin19.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id C93D51A0563 for ; Wed, 14 Oct 2026 13:49:16 +0000 (UTC) X-FDA: 85321363512.19.221EDD6 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf06.hostedemail.com (Postfix) with ESMTP id ED8DC18000B for ; Wed, 14 Oct 2026 13:49:14 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=PPzlrtN5; spf=pass (imf06.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1791985755; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=VlLY8lFnuENoZRIPsEzQ8Q4quedoDle8h5IdEqEOpQ8=; b=AIWHEpYIeENai3W8FXYK3IrYPJLikXlou+MR0B8JmdFCt1qPDwOwM7egXcknELc8sUlqLG R/lAcTWCtZklnSBiJRPp4DTGFxev+Re5qWcJQikHsQgAHk4OIEkKa5S9X71NmxlyT0FsXl 7Qj0guA5/pu48zxrZupr/v545PA9Csk= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=PPzlrtN5; spf=pass (imf06.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1791985755; b=P/UpJTZ6aKAtDa26EnizxpSn9yKGzcHa34Wl47taVOVOGdReqfE4D1AvX5E+VLjdvg4bEj fjcddW5PSBnxxszv6ZthWme/sd/pPYmSqa+8Pv7vtulBL8ie+tkJXc6wfpctiPhLzK9Mua DZCKLcBd4NHTNu8lOSQwT+Usrg5pkNQ= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 64FAE409F9; Wed, 14 Oct 2026 13:49:13 +0000 (UTC) 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 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 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: ED8DC18000B X-Rspam-User: X-Stat-Signature: ueziwwx987nauqomubiyteguytf3ug99 X-HE-Tag: 1791985754-780194 X-HE-Meta: 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 aUJIVoWW +JVFXqze+9C/qaAqF0TiKYaULNwmbhbVxyisIStW6i1Gr8TCjbuceXYV1K8T9Dg81wt2n6L9pBL42oob6huJS+cqDx4jHWVyQkfbLcy+3otov+zrqhe7tG1zdST8n5HcMFfxyrLSea+5HiohtzxjIANvoG9ApM0MFtqHDqREnskb7AK/l5LR67fnK2X8/sCP88NEmBnoh9hXpU+AOqsBZ3im8ShRObyJHumaaP2OSRKJ1YBFf66C4rhrqpCWBLNqcjInH/I34wjGZd2sTw7K6tWLFqherSDYsc8K/fwxN7iLEGjhZp/w9Dy7ZEz9ALMsPclRGFSlXkhmchu4G2fwsggNUH7nTgHHxgNME6NNN67e15Rawa9JQaBKR9IBlbzuCEiJc Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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