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 BC9BEC43458 for ; Mon, 13 Jul 2026 12:57:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 9AFA76B008C; Mon, 13 Jul 2026 08:57:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 986726B0092; Mon, 13 Jul 2026 08:57:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 89F886B0093; Mon, 13 Jul 2026 08:57:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 67F7E6B008C for ; Mon, 13 Jul 2026 08:57:27 -0400 (EDT) Received: from smtpin21.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay03.hostedemail.com (Postfix) with ESMTP id E4FC0A015A for ; Mon, 13 Jul 2026 12:57:26 +0000 (UTC) X-FDA: 84983754492.21.C87383F Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf02.hostedemail.com (Postfix) with ESMTP id 0E6E680007 for ; Mon, 13 Jul 2026 12:57:24 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FEOet2xl; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1783947445; 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=B9578WFJk2K+Q6hfVfJmltrDN/WRMnu0cbrC4CTiWnI=; b=RFPNcz5LU/ssbCAFlzrsYkOhh4jo6aGBOkxkPzLdlegzHE+iOp74GxlKW6Fx33omRymmnN KxGSSATzFFdfc2QCsx4JLGmYqFezpUa1nwA438cZPRZ0ItN3gkidGG5ZAsIrGmqSakN/zU ef624Ppv/N8rkPQOe+WpsMSp2C64jfU= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=FEOet2xl; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of david@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=david@kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783947445; b=qLQ2tvnK+NTiy+ZfWh/KBXnMPKvq3f6PywbzSAVmdlO7UQjey3hZ5VKFvrGYxX/8A2ukRo i0GVtBShC9/BBiVvS4TTqYrqDjivPnRIOOoG1v+9dFpSh7H9D2JQFdXpccsKZK9GSJbPah oCm9EFUtMJ/sxSbsduOA5WVWbgWdqAk= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 325AE417E2; Mon, 13 Jul 2026 12:57:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0EDF1F00A3E; Mon, 13 Jul 2026 12:57:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783947444; bh=B9578WFJk2K+Q6hfVfJmltrDN/WRMnu0cbrC4CTiWnI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FEOet2xl60iiJk7uxbnnVR32Bo8fASIfZBQV+QxoTmwT2ow5ZUvdO+3PwRrn08x7S 98l87O64FycK3x37Pujc/PM11bNCPkB+RqUVrSnLiGB39vQTuTDcTZiuzh6DOs3wsm FJjaO3V0l0+7SOG6+KEbFHmuRjdrPvvWUp7HfmoTnc2RMh4O6XBfXr6nJzT0b36ieo PLmSVKAN5uIL7/x8jUdIycvTYZxfgpPRq8lx7gSnnp6wZplV4L3/h8MvFm+meU3oZp gUkQWRQn50N52Cpc30bof5XTYbbDZWC0HX711UwhFlFpgLxMXqKWYqU3DGW4U8Bsij DDHqKhlat0aIg== Message-ID: Date: Mon, 13 Jul 2026 14:57:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate_device: avoid overflowing migrate_vma collection arrays To: Zi Yan , Andrew Morton , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Balbir Singh , Kefeng Wang Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Sashiko References: <20260707-fix-array-overflow-in-migrate_vma_collect_pmd-v1-1-ce3ff4627653@nvidia.com> <89d20411-4915-43e8-9808-3a7fbd98d2ab@kernel.org> 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-Stat-Signature: pemmex5anzc5y4w6poz7c3q99na89xyk X-Rspamd-Queue-Id: 0E6E680007 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1783947444-794222 X-HE-Meta: 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 Wsfl5sGG CT4WiobYo97LdlamWqursBmAFxZInz6nHpbj/xDGbIr+WqxMU09+PDYJlLd/rVsp57Wkl42gjgH3eyzZpMRocHOT7bW24SnA3AEPoEO2OpBjYeGdSUsGJjKx5cM9u+lak8WGCGbgBPdqiuPAuNocUzk+dMJpXX7l7/B9frSME2C0It7voAuIvlBb4p8C56YGxRpysoDUYcaJmiqaeOYo8oy5HgGC7Revvl6k/oDUI07oFJA/W/AVDgcxFN5WCJcgXs9/2MTGpcnzacogIWQTflwRa8Tt9jtQzzKTDnZyASibFZqaz+hMVnztthAU/EMvAOH+ar64/CCdHDIetfwLT9nKKOYgXdkTfuvnhP1BmWUv5q+UPENEZidrUpKzz2hI7GGHu Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/10/26 17:35, Zi Yan wrote: > On Fri Jul 10, 2026 at 7:56 AM EDT, David Hildenbrand (Arm) wrote: >> On 7/10/26 13:30, Zi Yan wrote: >>> >>> Hi David, >>> >> >> Hi, >> >>> Do you think this patch is good to get in? I would like to get ack from >>> you. >> >> I dislike that we fail collecting even though there is something (different) >> mapped now. > > Not all the time. After a folio split and PTE lock is dropped, there are > different cases: > > 1. no page table change, the collection grabs the PTE lock and continues; Yes. > > 2. some PTE(s) is changed, the same as 1 and the collection continues; Yes. > > 3. the PMD pointing to the PTE page table is changed to either a leaf > PMD or an invalid PMD, the collection cannot grab the PTE lock to > work on the remaming PTEs, since they are gone. For the collected > PFNs (they are mapped more than once) and folios with elevated > refcount (they are mapped once and unmapped here as an optimization), > they will be processed later in migrate_vma_unmap(). Since > migrate_vma_collect() is best effort, there is no need to revert and > try to recollect from the beginning (to get that possible large > folio or skip). Yes. > > BTW, recollection will be more feasible if migrate_vma_collect() does > not do unmap singly-mapped optimization, since in the case, no PTE is > changed, we just need to reset migrate->->cpages and migrate->npages and > restart from the beginning. > >> >> In case we stumble over a PMD, there sure are no migration entries on the PTE >> level anymore? > > Right. The PTE page table should be gone and the original PMD, pointing > to the PTE page table, becomes a leaf PMD or an invalid PMD, since > someone changed it when the PTE lock is dropped. Right, so I guess we'd have to remember how far to rollback, and rollback would mean resetting migrate->->cpages and migrate->npages. And for the entries we rollback, we have to decide whether to folio_put() and whether to folio_unlock() [fault_folio != folio]. That's the confusing bit given that the code is rather "interesting". -- Cheers, David