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Thu, 22 Jan 2026 06:28:13 -0500 (EST) Date: Thu, 22 Jan 2026 11:28:06 +0000 From: Kiryl Shutsemau To: Muchun Song Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCHv4 07/14] mm/sparse: Check memmap alignment for compound_info_has_mask() Message-ID: References: <20260121162253.2216580-1-kas@kernel.org> <20260121162253.2216580-8-kas@kernel.org> <71F051F2-5F3B-40A5-9347-BA2D93F2FF3F@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <71F051F2-5F3B-40A5-9347-BA2D93F2FF3F@linux.dev> On Thu, Jan 22, 2026 at 11:10:26AM +0800, Muchun Song wrote: > > > > On Jan 22, 2026, at 00:22, Kiryl Shutsemau wrote: > > > > If page->compound_info encodes a mask, it is expected that memmap to be > > naturally aligned to the maximum folio size. > > > > Add a warning if it is not. > > > > A warning is sufficient as MAX_FOLIO_ORDER is very rarely used, so the > > kernel is still likely to be functional if this strict check fails. > > > > Signed-off-by: Kiryl Shutsemau > > --- > > include/linux/mmzone.h | 1 + > > mm/sparse.c | 5 +++++ > > 2 files changed, 6 insertions(+) > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index 390ce11b3765..7e4f69b9d760 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -91,6 +91,7 @@ > > #endif > > > > #define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER) > > +#define MAX_FOLIO_SIZE (PAGE_SIZE << MAX_FOLIO_ORDER) > > > > enum migratetype { > > MIGRATE_UNMOVABLE, > > diff --git a/mm/sparse.c b/mm/sparse.c > > index 17c50a6415c2..5f41a3edcc24 100644 > > --- a/mm/sparse.c > > +++ b/mm/sparse.c > > @@ -600,6 +600,11 @@ void __init sparse_init(void) > > BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section))); > > memblocks_present(); > > > > + if (compound_info_has_mask()) { > > + WARN_ON(!IS_ALIGNED((unsigned long)pfn_to_page(0), > > + MAX_FOLIO_SIZE / sizeof(struct page))); > > I still have concerns about this. If certain architectures or configurations, > especially when KASLR is enabled, do not meet the requirements during the > boot stage, only specific folios larger than a certain size might end up with > incorrect struct page entries as the system runs. How can we detect issues > arising from either updating the struct page or making incorrect logical > judgments based on information retrieved from the struct page? > > After all, when we see this warning, we don't know when or if a problem will > occur in the future. It's like a time bomb in the system, isn't it? Therefore, > I would like to add a warning check to the memory allocation place, for > example: > > WARN_ON(!IS_ALIGNED((unsigned long)&folio->page, folio_size / sizeof(struct page))); I don't think it is needed. Any compound page usage would trigger the problem. It should happen pretty early. -- Kiryl Shutsemau / Kirill A. Shutemov