FAILED: patch "[PATCH] mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x cd681403a87085562499d60325b7b45d3be11217
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072046-viewable-richness-35ef@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From cd681403a87085562499d60325b7b45d3be11217 Mon Sep 17 00:00:00 2001
From: Muchun Song <[email protected]>
Date: Tue, 28 Apr 2026 16:18:55 +0800
Subject: [PATCH] mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE

If DAX memory is hotplugged into an unoccupied subsection of an early section, section_activate() reuses the unoptimized boot memmap. However, compound_nr_pages() still assumes that vmemmap optimization is in effect and initializes only the reduced number of struct pages. As a result, the remaining tail struct pages are left uninitialized, which can later lead to unexpected behavior or crashes.

Fix this by treating early sections as unoptimized when calculating how many struct pages to initialize.

index cfc76953e249..bd466a3c10c8 100644
@@ -1055,10 +1055,17 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
  * of how the sparse_vmemmap internals handle compound pages in the lack
  * of an altmap. See vmemmap_populate_compound_pages().
  */
-static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
+static inline unsigned long compound_nr_pages(unsigned long pfn,
+					      struct vmem_altmap *altmap,
 					      struct dev_pagemap *pgmap)
 {
-	if (!vmemmap_can_optimize(altmap, pgmap))
+	/*
+	 * If DAX memory is hot-plugged into an unoccupied subsection
+	 * of an early section, the unoptimized boot memmap is reused.
+	 * See section_activate().
+	 */
+	if (early_section(__pfn_to_section(pfn)) ||
+	    !vmemmap_can_optimize(altmap, pgmap))
 		return pgmap_vmemmap_nr(pgmap);
 
 	return VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page));

@@ -1128,7 +1135,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 			continue;
 
 		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
-				     compound_nr_pages(altmap, pgmap));
+				     compound_nr_pages(pfn, altmap, pgmap));
 	}
 
 	pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);

From: "Mike Rapoport (IBM)" <[email protected]>

[ Upstream commit 9420f89db2dd611c5b436a13e13f74d65ecc3a6a ]

The bulk of memory management initialization code is spread all over mm/page_alloc.c and makes navigating through page allocator functionality difficult.

Move most of the functions marked __init and __meminit to mm/mm_init.c to make it better localized and allow some more spare room before mm/page_alloc.c reaches 10k lines.

No functional changes.

Stable-dep-of: cd681403a870 ("mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE")

---
 mm/internal.h   |   4 ++
 mm/mm_init.c    | 154 ++++++++++++++++++++++++++++++++++++++++++++++++
 mm/page_alloc.c | 144 ++------------------------------------------
 3 files changed, 162 insertions(+), 140 deletions(-)

index 16a4a9aece3043..3e3dfc8e0bc6ab 100644
@@ -389,6 +389,10 @@ extern void __putback_isolated_page(struct page *page, unsigned int order,
 extern void memblock_free_pages(struct page *page, unsigned long pfn,
 					unsigned int order);
 extern void __free_pages_core(struct page *page, unsigned int order);
+void __init_single_page(struct page *page, unsigned long pfn,
+			unsigned long zone, int nid);
+void prep_compound_head(struct page *page, unsigned int order);
+void prep_compound_tail(struct page *head, int tail_idx);
 extern void prep_compound_page(struct page *page, unsigned int order);
 extern void post_alloc_hook(struct page *page, unsigned int order,
 					gfp_t gfp_flags);

2.53.0

From: "Aneesh Kumar K.V" <[email protected]>

[ Upstream commit 87a7ae75d7383afa998f57656d1d14e2a730cc47 ]

commit 4917f55b4ef9 ("mm/sparse-vmemmap: improve memory savings for compound devmaps") added support for using optimized vmmemap for devdax devices. But how vmemmap mappings are created are architecture specific. For example, powerpc with hash translation doesn't have vmemmap mappings in init_mm page table instead they are bolted table entries in the hardware page table

vmemmap_populate_compound_pages() used by vmemmap optimization code is not aware of these architecture-specific mapping. Hence allow architecture to opt for this feature. I selected architectures supporting HUGETLB_PAGE_OPTIMIZE_VMEMMAP option as also supporting this feature.

This patch fixes the below crash on ppc64.

BUG: Unable to handle kernel data access on write at 0xc00c000100400038
Faulting instruction address: 0xc000000001269d90
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries
Modules linked in:
CPU: 7 PID: 1 Comm: swapper/0 Not tainted 6.3.0-rc5-150500.34-default+ #2 5c90a668b6bbd142599890245c2fb5de19d7d28a
Hardware name: IBM,9009-42G POWER9 (raw) 0x4e0202 0xf000005 of:IBM,FW950.40 (VL950_099) hv:phyp pSeries
NIP:  c000000001269d90 LR: c0000000004c57d4 CTR: 0000000000000000
REGS: c000000003632c30 TRAP: 0300   Not tainted  (6.3.0-rc5-150500.34-default+)
MSR:  8000000000009033 <SF,EE,ME,IR,DR,RI,LE>  CR: 24842228  XER: 00000000
CFAR: c0000000004c57d0 DAR: c00c000100400038 DSISR: 42000000 IRQMASK: 0
....
NIP [c000000001269d90] __init_single_page.isra.74+0x14/0x4c
LR [c0000000004c57d4] __init_zone_device_page+0x44/0xd0
Call Trace:

[c000000003632ed0] [c000000003632f60] 0xc000000003632f60 (unreliable) [c000000003632f10] [c0000000004c5ca0] memmap_init_zone_device+0x170/0x250 [c000000003632fe0] [c0000000005575f8] memremap_pages+0x2c8/0x7f0 [c0000000036330c0] [c000000000557b5c] devm_memremap_pages+0x3c/0xa0 [c000000003633100] [c000000000d458a8] dev_dax_probe+0x108/0x3e0 [c0000000036331a0] [c000000000d41430] dax_bus_probe+0xb0/0x140 [c0000000036331d0] [c000000000cef27c] really_probe+0x19c/0x520 [c000000003633260] [c000000000cef6b4] __driver_probe_device+0xb4/0x230 [c0000000036332e0] [c000000000cef888] driver_probe_device+0x58/0x120 [c000000003633320] [c000000000cefa6c] __device_attach_driver+0x11c/0x1e0 [c0000000036333a0] [c000000000cebc58] bus_for_each_drv+0xa8/0x130 [c000000003633400] [c000000000ceefcc] __device_attach+0x15c/0x250 [c0000000036334a0] [c000000000ced458] bus_probe_device+0x108/0x110 [c0000000036334f0] [c000000000ce92dc] device_add+0x7fc/0xa10 [c0000000036335b0] [c000000000d447c8] devm_create_dev_dax+0x1d8/0x530 [c000000003633640] [c000000000d46b60] __dax_pmem_probe+0x200/0x270 [c0000000036337b0] [c000000000d46bf0] dax_pmem_probe+0x20/0x70 [c0000000036337d0] [c000000000d2279c] nvdimm_bus_probe+0xac/0x2b0 [c000000003633860] [c000000000cef27c] really_probe+0x19c/0x520 [c0000000036338f0] [c000000000cef6b4] __driver_probe_device+0xb4/0x230 [c000000003633970] [c000000000cef888] driver_probe_device+0x58/0x120 [c0000000036339b0] [c000000000cefd08] __driver_attach+0x1d8/0x240 [c000000003633a30] [c000000000cebb04] bus_for_each_dev+0xb4/0x130 [c000000003633a90] [c000000000cee564] driver_attach+0x34/0x50 [c000000003633ab0] [c000000000ced878] bus_add_driver+0x218/0x300 [c000000003633b40] [c000000000cf1144] driver_register+0xa4/0x1b0 [c000000003633bb0] [c000000000d21a0c] __nd_driver_register+0x5c/0x100 [c000000003633c10] [c00000000206a2e8] dax_pmem_init+0x34/0x48 [c000000003633c30] [c0000000000132d0] do_one_initcall+0x60/0x320 [c000000003633d00] [c0000000020051b0] kernel_init_freeable+0x360/0x400 [c000000003633de0] [c000000000013764] kernel_init+0x34/0x1d0 [c000000003633e50] [c00000000000de14] ret_from_kernel_thread+0x5c/0x64

Stable-dep-of: cd681403a870 ("mm/mm_init: fix uninitialized struct pages for ZONE_DEVICE")

---
 include/linux/mm.h  | 12 ++++++++++++
 mm/mm_init.c        | 11 -----------
 mm/sparse-vmemmap.c |  3 +--
 3 files changed, 13 insertions(+), 13 deletions(-)

index ac0638a8c38dba..4f0aa81257c585 100644
@@ -3405,6 +3405,18 @@ void vmemmap_populate_print_last(void);
 void vmemmap_free(unsigned long start, unsigned long end,
 		struct vmem_altmap *altmap);
 #endif
+
+#define VMEMMAP_RESERVE_NR	2
+#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+#define vmemmap_can_optimize(altmap, pgmap)				\
+	(is_power_of_2(sizeof(struct page)) && (pgmap) && !(altmap) &&	\
+	 (((pgmap_vmemmap_nr(pgmap) * sizeof(struct page)) >> PAGE_SHIFT) > \
+	  VMEMMAP_RESERVE_NR))
+#else
+#define vmemmap_can_optimize(altmap, pgmap)	\
+	((void)(altmap), (void)(pgmap), false)
+#endif
+
 void register_page_bootmem_memmap(unsigned long section_nr, struct page *map,
 				  unsigned long nr_pages);
 

index ccfccb45808ab1..5aab6903bddcbe 100644
@@ -241,17 +241,6 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn,
 		set_page_count(page, 0);
 }
 
-#define VMEMMAP_RESERVE_NR	2
-#ifdef CONFIG_ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
-#define vmemmap_can_optimize(altmap, pgmap)				\
-	(is_power_of_2(sizeof(struct page)) && !(altmap) &&		\
-	 (((pgmap_vmemmap_nr(pgmap) * sizeof(struct page)) >> PAGE_SHIFT) > \
-	  VMEMMAP_RESERVE_NR))
-#else
-#define vmemmap_can_optimize(altmap, pgmap)	\
-	((void)(altmap), (void)(pgmap), false)
-#endif
-
 #define pageblock_migratetype_init_range(start_pfn, nr_pages, migratetype) \
 do {									\
 	unsigned long __start = (start_pfn);				\

index f89dbaa05eef3e..28929fdf5d3bca 100644
@@ -385,8 +385,7 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		!IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION)))
 		return NULL;
 
-	if (is_power_of_2(sizeof(struct page)) &&
-	    pgmap && pgmap_vmemmap_nr(pgmap) > 1 && !altmap)
+	if (vmemmap_can_optimize(altmap, pgmap))
 		r = vmemmap_populate_compound_pages(pfn, start, end, nid, pgmap);
 	else
 		r = vmemmap_populate(start, end, nid, altmap);

2.53.0

From: Muchun Song <[email protected]>

[ Upstream commit cd681403a87085562499d60325b7b45d3be11217 ]

If DAX memory is hotplugged into an unoccupied subsection of an early section, section_activate() reuses the unoptimized boot memmap. However, compound_nr_pages() still assumes that vmemmap optimization is in effect and initializes only the reduced number of struct pages. As a result, the remaining tail struct pages are left uninitialized, which can later lead to unexpected behavior or crashes.

Fix this by treating early sections as unoptimized when calculating how many struct pages to initialize.

---
 mm/mm_init.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

index 5aab6903bddcbe..a3acd113e7d0a4 100644
@@ -262,10 +262,17 @@ do {									\
  * of how the sparse_vmemmap internals handle compound pages in the lack
  * of an altmap. See vmemmap_populate_compound_pages().
  */
-static inline unsigned long compound_nr_pages(struct vmem_altmap *altmap,
+static inline unsigned long compound_nr_pages(unsigned long pfn,
+					      struct vmem_altmap *altmap,
 					      struct dev_pagemap *pgmap)
 {
-	if (!vmemmap_can_optimize(altmap, pgmap))
+	/*
+	 * If DAX memory is hot-plugged into an unoccupied subsection
+	 * of an early section, the unoptimized boot memmap is reused.
+	 * See section_activate().
+	 */
+	if (early_section(__pfn_to_section(pfn)) ||
+	    !vmemmap_can_optimize(altmap, pgmap))
 		return pgmap_vmemmap_nr(pgmap);
 
 	return VMEMMAP_RESERVE_NR * (PAGE_SIZE / sizeof(struct page));

@@ -338,7 +345,7 @@ void __ref memmap_init_zone_device(struct zone *zone,
 			continue;
 
 		memmap_init_compound(page, pfn, zone_idx, nid, pgmap,
-				     compound_nr_pages(altmap, pgmap));
+				     compound_nr_pages(pfn, altmap, pgmap));
 	}
 
 	pageblock_migratetype_init_range(start_pfn, nr_pages, MIGRATE_MOVABLE);

2.53.0