+ mm-warn-on-unaligned-compound-zone-device-ranges.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: warn on unaligned compound zone device ranges
has been added to the -mm mm-unstable branch.  Its filename is
     mm-warn-on-unaligned-compound-zone-device-ranges.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-warn-on-unaligned-compound-zone-device-ranges.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Muchun Song <muchun.song@linux.dev>
Subject: mm: warn on unaligned compound zone device ranges
Date: Fri, 16 Oct 2026 21:13:34 +0800

A compound page of order N must start at a PFN aligned to 2^N pages. 
Therefore, a range used to initialize compound pages must start on a
compound-page boundary and contain an integral number of compound pages.

Two recent Device DAX bugs were caused by ranges that violated this
invariant, but neither was detected by memmap_init_zone_device().

Warn if the adjusted zone-device range violates this invariant so future
violations are reported when the compound pages are initialized.

Link: https://lore.kernel.org/20261016131334.3419393-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/r/20261016053944.2579541-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/r/20261016054914.2601510-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Assisted-by: LLM
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---

 mm/mm_init.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/mm_init.c~mm-warn-on-unaligned-compound-zone-device-ranges
+++ a/mm/mm_init.c
@@ -1142,6 +1142,8 @@ void __ref memmap_init_zone_device(struc
 	if (!nr_pages)
 		return;
 
+	VM_WARN_ON(!IS_ALIGNED(start_pfn | nr_pages, pfns_per_compound));
+
 	/*
 	 * Seed the reusable head-page template from the first real struct
 	 * page. The normal page-init and refcount helpers must operate on
_

Patches currently in -mm which might be from muchun.song@linux.dev are

mm-sparse-vmemmap-drop-vmemmap_populate_dax.patch
mm-sparse-vmemmap-support-device-dax-in-common-vmemmap-path.patch
mm-sparse-vmemmap-drop-device-dax-specific-population-path.patch
mm-sparse-vmemmap-remove-the-unused-ptpfn-argument.patch
mm-sparse-vmemmap-open-code-vmemmap_populate_address.patch
mm-mm_init-add-zone-mismatch-warning-during-page-init.patch
mm-mm_init-add-zone-mismatch-warning-during-page-init-fix.patch
mm-fix-missing-page-table-destructor-in-pagetable_free.patch
arm64-mm-fix-destructor-for-unconstructed-hotplug-page-tables.patch
mm-warn-on-unaligned-compound-zone-device-ranges.patch