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ARM: 9524/1: mm: align hugetlb mappings to the huge page size

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mmap(MAP_HUGETLB) on 32-bit Arm can return an address which is not
aligned to the huge page size. In a QEMU virt guest, unmapping the VMA
then hits the alignment check in __unmap_hugepage_range():

  kernel BUG at mm/hugetlb.c:5213!
  Internal error: Oops - BUG: 0 [#1] SMP ARM
  PC is at __unmap_hugepage_range+0x540/0x584
  LR is at __zap_vma_range+0x13a0/0x1410

Commit 7bd3f1e1a9 ("mm: make hugetlb mappings go through
mm_get_unmapped_area_vmflags") made hugetlb mappings use the
architecture's arch_get_unmapped_area(). The generic implementations
handle hugetlb alignment, but the Arm implementations only account for
the optional SHMLBA cache-colouring constraint. A 4 KiB-page kernel can
therefore align the mapping to 4 KiB or 16 KiB instead of the required
2 MiB.

Set the alignment mask from the file's hstate for hugetlb mappings in
both Arm implementations. Huge-page alignment also satisfies the
SHMLBA constraint.

Assisted-by: LLM

Fixes: 7bd3f1e1a9 ("mm: make hugetlb mappings go through mm_get_unmapped_area_vmflags")
Cc: stable@vger.kernel.org
Acked-by: Muchun Song <muchun.song@linux.dev>
Link: https://lore.kernel.org/r/20260901085740.66283-1-kmehltretter@gmail.com/
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Karl Mehltretter 2026-09-26 17:06:03 +01:00 committed by Russell King
parent 2d4234f999
commit 1eb87d8f77
1 changed files with 9 additions and 2 deletions
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11
arch/arm/mm/mmap.c
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@ -11,6 +11,7 @@
#include <linux/io.h>
#include <linux/personality.h>
#include <linux/random.h>
#include <linux/hugetlb.h>
#include <asm/cachetype.h>
#define COLOUR_ALIGN(addr,pgoff) \
@ -72,7 +73,10 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
info.length = len;
info.low_limit = mm->mmap_base;
info.high_limit = TASK_SIZE;
info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
if (filp && is_file_hugepages(filp))
info.align_mask = huge_page_mask_align(filp);
else
info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
info.align_offset = pgoff << PAGE_SHIFT;
return vm_unmapped_area(&info);
}
@ -123,7 +127,10 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
info.length = len;
info.low_limit = FIRST_USER_ADDRESS;
info.high_limit = mm->mmap_base;
info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
if (filp && is_file_hugepages(filp))
info.align_mask = huge_page_mask_align(filp);
else
info.align_mask = do_align ? (PAGE_MASK & (SHMLBA - 1)) : 0;
info.align_offset = pgoff << PAGE_SHIFT;
addr = vm_unmapped_area(&info);