The patch titled Subject: mm/memblock: correct totalram_pages accounting with KMSAN has been added to the -mm mm-new branch. Its filename is mm-memblock-correct-totalram_pages-accounting-with-kmsan.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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

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------------------------------------------------------ From: Alexander Potapenko glider@google.com Subject: mm/memblock: correct totalram_pages accounting with KMSAN Date: Wed, 24 Sep 2025 12:03:01 +0200

When KMSAN is enabled, `kmsan_memblock_free_pages()` can hold back pages for metadata instead of returning them to the early allocator. The callers, however, would unconditionally increment `totalram_pages`, assuming the pages were always freed. This resulted in an incorrect calculation of the total available RAM, causing the kernel to believe it had more memory than it actually did.

This patch refactors `memblock_free_pages()` to return the number of pages it successfully frees. If KMSAN stashes the pages, the function now returns 0; otherwise, it returns the number of pages in the block.

The callers in `memblock.c` have been updated to use this return value, ensuring that `totalram_pages` is incremented only by the number of pages actually returned to the allocator. This corrects the total RAM accounting when KMSAN is active.

Link: https://lkml.kernel.org/r/20250924100301.1558645-1-glider@google.com Fixes: 3c2065098260 ("init: kmsan: call KMSAN initialization routines") Signed-off-by: Alexander Potapenko glider@google.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Aleksandr Nogikh nogikh@google.com Cc: Dmitriy Vyukov dvyukov@google.com Cc: Marco Elver elver@google.com Cc: Markus Elfring Markus.Elfring@web.de Cc: Mike Rapoport rppt@kernel.org Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/internal.h | 4 ++-- mm/memblock.c | 21 +++++++++++---------- mm/mm_init.c | 9 +++++---- 3 files changed, 18 insertions(+), 16 deletions(-)

--- a/mm/internal.h~mm-memblock-correct-totalram_pages-accounting-with-kmsan +++ a/mm/internal.h @@ -742,8 +742,8 @@ static inline void clear_zone_contiguous extern int __isolate_free_page(struct page *page, unsigned int order); extern void __putback_isolated_page(struct page *page, unsigned int order, int mt); -extern void memblock_free_pages(struct page *page, unsigned long pfn, - unsigned int order); +unsigned long memblock_free_pages(struct page *page, unsigned long pfn, + unsigned int order); extern void __free_pages_core(struct page *page, unsigned int order, enum meminit_context context);

--- a/mm/memblock.c~mm-memblock-correct-totalram_pages-accounting-with-kmsan +++ a/mm/memblock.c @@ -1826,6 +1826,7 @@ void *__init __memblock_alloc_or_panic(p void __init memblock_free_late(phys_addr_t base, phys_addr_t size) { phys_addr_t cursor, end; + unsigned long freed_pages = 0;

end = base + size - 1; memblock_dbg("%s: [%pa-%pa] %pS\n", @@ -1834,10 +1835,9 @@ void __init memblock_free_late(phys_addr cursor = PFN_UP(base); end = PFN_DOWN(base + size);

- for (; cursor < end; cursor++) { - memblock_free_pages(pfn_to_page(cursor), cursor, 0); - totalram_pages_inc(); - } + for (; cursor < end; cursor++) + freed_pages += memblock_free_pages(pfn_to_page(cursor), cursor, 0); + totalram_pages_add(freed_pages); }

/* @@ -2259,9 +2259,11 @@ static void __init free_unused_memmap(vo #endif }

-static void __init __free_pages_memory(unsigned long start, unsigned long end) +static unsigned long __init __free_pages_memory(unsigned long start, + unsigned long end) { int order; + unsigned long freed = 0;

while (start < end) { /* @@ -2279,14 +2281,15 @@ static void __init __free_pages_memory(u while (start + (1UL << order) > end) order--;

- memblock_free_pages(pfn_to_page(start), start, order); + freed += memblock_free_pages(pfn_to_page(start), start, order);

start += (1UL << order); } + return freed; }

static unsigned long __init __free_memory_core(phys_addr_t start, - phys_addr_t end) + phys_addr_t end) { unsigned long start_pfn = PFN_UP(start); unsigned long end_pfn = PFN_DOWN(end); @@ -2297,9 +2300,7 @@ static unsigned long __init __free_memor if (start_pfn >= end_pfn) return 0;

- __free_pages_memory(start_pfn, end_pfn); - - return end_pfn - start_pfn; + return __free_pages_memory(start_pfn, end_pfn); }

static void __init memmap_init_reserved_pages(void) --- a/mm/mm_init.c~mm-memblock-correct-totalram_pages-accounting-with-kmsan +++ a/mm/mm_init.c @@ -2547,24 +2547,25 @@ void *__init alloc_large_system_hash(con return table; }

-void __init memblock_free_pages(struct page *page, unsigned long pfn, - unsigned int order) +unsigned long __init memblock_free_pages(struct page *page, unsigned long pfn, + unsigned int order) { if (IS_ENABLED(CONFIG_DEFERRED_STRUCT_PAGE_INIT)) { int nid = early_pfn_to_nid(pfn);

if (!early_page_initialised(pfn, nid)) - return; + return 0; }

if (!kmsan_memblock_free_pages(page, order)) { /* KMSAN will take care of these pages. */ - return; + return 0; }

/* pages were reserved and not allocated */ clear_page_tag_ref(page); __free_pages_core(page, order, MEMINIT_EARLY); + return 1UL << order; }

DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc); _

Patches currently in -mm which might be from glider@google.com are

mm-memblock-correct-totalram_pages-accounting-with-kmsan.patch