[{"id":3681865,"web_url":"http://patchwork.ozlabs.org/comment/3681865/","msgid":"","date":"2026-04-24T08:20:20","subject":"Re: [PATCH v6 6/7] mm/mm_init: Fix uninitialized struct pages for\n ZONE_DEVICE","submitter":{"id":77733,"url":"http://patchwork.ozlabs.org/api/people/77733/","name":"Mike Rapoport","email":"rppt@kernel.org"},"content":"On Fri, Apr 24, 2026 at 10:55:46AM +0800, Muchun Song wrote:\n> If DAX memory is hotplugged into an unoccupied subsection of an early\n> section, section_activate() reuses the unoptimized boot memmap.\n> However, compound_nr_pages() still assumes that vmemmap optimization is\n> in effect and initializes only the reduced number of struct pages. As a\n> result, the remaining tail struct pages are left uninitialized, which\n> can later lead to unexpected behavior or crashes.\n> \n> Fix this by treating early sections as unoptimized when calculating how\n> many struct pages to initialize.\n> \n> Fixes: 6fd3620b3428 (\"mm/page_alloc: reuse tail struct pages for compound devmaps\")\n> Cc: stable@vger.kernel.org\n> Signed-off-by: Muchun Song \n> Acked-by: David Hildenbrand (Arm) \n\nAcked-by: Mike Rapoport (Microsoft) \n\n> ---\n> mm/mm_init.c | 13 ++++++++++---\n> 1 file changed, 10 insertions(+), 3 deletions(-)\n> \n> diff --git a/mm/mm_init.c b/mm/mm_init.c\n> index cfc76953e249..bd466a3c10c8 100644\n> --- a/mm/mm_init.c\n> +++ b/mm/mm_init.c\n> @@ -1055,10 +1055,17 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,\n> * of how the sparse_vmemmap internals handle compound pages in the lack\n> * of an altmap. See vmemmap_populate_compound_pages().\n> */\n> -static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,\n> +static inline unsigned long compound_nr_pages(unsigned long pfn,\n> +\t\t\t\t\t struct vmem_altmap *altmap,\n> \t\t\t\t\t struct dev_pagemap *pgmap)\n> {\n> -\tif (!vmemmap_can_optimize(altmap, pgmap))\n> +\t/*\n> +\t * If DAX memory is hot-plugged into an unoccupied subsection\n> +\t * of an early section, the unoptimized boot memmap is reused.\n> +\t * See section_activate().\n> +\t */\n> +\tif (early_section(__pfn_to_section(pfn)) ||\n> +\t !vmemmap_can_optimize(altmap, pgmap))\n> \t\treturn pgmap_vmemmap_nr(pgmap);\n> \n> \treturn VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page));\n> @@ -1128,7 +1135,7 @@ void __ref memmap_init_zone_device(struct zone *zone,\n> \t\t\tcontinue;\n> \n> \t\tmemmap_init_compound(page, pfn, zone_idx, nid, pgmap,\n> -\t\t\t\t compound_nr_pages(altmap, pgmap));\n> +\t\t\t\t compound_nr_pages(pfn, altmap, pgmap));\n> \t}\n> \n> \tpageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);\n> -- \n> 2.20.1\n>","headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linuxppc-dev@lists.ozlabs.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=mOMKksAU;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=lists.ozlabs.org\n (client-ip=112.213.38.117; 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Howlett\" ,\n\tVlastimil Babka ,\n\tSuren Baghdasaryan ,\n\tMichal Hocko , Nicholas Piggin ,\n\tChristophe Leroy , aneesh.kumar@linux.ibm.com,\n\tjoao.m.martins@oracle.com, linux-mm@kvack.org,\n\tlinuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,\n\tstable@vger.kernel.org","Subject":"Re: [PATCH v6 6/7] mm/mm_init: Fix uninitialized struct pages for\n ZONE_DEVICE","Message-ID":"","References":"<20260424025547.3806072-1-songmuchun@bytedance.com>\n <20260424025547.3806072-7-songmuchun@bytedance.com>","X-Mailing-List":"linuxppc-dev@lists.ozlabs.org","List-Id":"","List-Help":"","List-Owner":"","List-Post":"","List-Archive":",\n ","List-Subscribe":",\n ,\n ","List-Unsubscribe":"","Precedence":"list","MIME-Version":"1.0","Content-Type":"text/plain; charset=us-ascii","Content-Disposition":"inline","In-Reply-To":"<20260424025547.3806072-7-songmuchun@bytedance.com>","X-Spam-Status":"No, score=-0.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED,\n\tDKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS\n\tautolearn=disabled version=4.0.1 OzLabs 8","X-Spam-Checker-Version":"SpamAssassin 4.0.1 (2024-03-25) on lists.ozlabs.org"}}]