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| author | Chen Wandun <chenwandun@lixiang.com> | 2026-05-13 13:54:28 +0800 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-05-28 21:31:55 -0700 |
| commit | ce6133eea67fd206cb034e8e5ffbb4ad687e3f77 (patch) | |
| tree | b80fc55d31a3663af6d15ad5885ccc2caf488db1 | |
| parent | aa37d2738f714edcdf1c7c83d5a2b788122978a4 (diff) | |
| download | linux-next-history-ce6133eea67fd206cb034e8e5ffbb4ad687e3f77.tar.gz | |
mm/khugepaged: avoid underflow in madvise_collapse for sub-PMD MADV_COLLAPSE
madvise_collapse() computes the THP-aligned window:
hstart = ALIGN(start, HPAGE_PMD_SIZE); /* round up */
hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); /* round down */
The following case will cause hstart > hend, and result in underflow in
the return statement, avoid it by returning zero early when hstart > hend.
The return value is due to input is valid to madvise(), and there is
nothing to collapse.
madvise(PMD-aligned + PAGE_SIZE, PAGE_SIZE, MADV_COLLAPSE);
In addition, kmalloc_obj(), mmgrab() and lru_add_drain_all() are
unnecessary when hstart == hend, so skip these operations by returning
early too.
Link: https://lore.kernel.org/20260513055428.1664898-1-chenwandun@lixiang.com
Signed-off-by: Chen Wandun <chenwandun@lixiang.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/khugepaged.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 792ea275541f9..35a5f8c44c181 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -3207,6 +3207,12 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, if (!collapse_allowable_orders(vma, vma->vm_flags, TVA_FORCED_COLLAPSE)) return -EINVAL; + hstart = ALIGN(start, HPAGE_PMD_SIZE); + hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); + + if (hstart >= hend) + return 0; + cc = kmalloc_obj(*cc); if (!cc) return -ENOMEM; @@ -3216,9 +3222,6 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start, mmgrab(mm); lru_add_drain_all(); - hstart = ALIGN(start, HPAGE_PMD_SIZE); - hend = ALIGN_DOWN(end, HPAGE_PMD_SIZE); - for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) { enum scan_result result = SCAN_FAIL; |