6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: SJ Park [ Upstream commit 946351a5fc5d4e3afec2bdf735935d17d6c9ceb2 ] For applying DAMOS_STAT action to a region, DAMON virtual address space operation set (vaddr) calls walk_page_range[_vma]() for the region. The pmd walk entry function, namely damon_va_stat_pmd_entry(), applies DAMOS filters to folios of addresses of the region in the pmd. It starts from the walking address and advances the address by the size of the folio of the address until it goes out of the pmd or the region. Let's suppose it is for the first pmd of the region, and the region start address is in the middle of a large folio. Also, the next folios are small. Then, some of the next folios could be skipped. Fix the issue by advancing the address to exactly the start address of the next folio. The user impact is that the DAMOS_STAT-based page level monitoring results become inaccurate. Since the page level monitoring is supposed to provide relatively high precision, this is definitely a problem. It is arguably not critical since it is only monitoring quality degradation. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20260901131850.98037-5-sj@kernel.org Link: https://lore.kernel.org/20260514015053.149396-1-sj@kernel.org [1] Fixes: 63f39737d1e3 ("mm/damon/vaddr: support stat-purpose DAMOS filters") Signed-off-by: SJ Park Signed-off-by: Andrew Morton Cc: Usama Arif Cc: # 6.18.x Signed-off-by: Sasha Levin --- mm/damon/vaddr.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index cfa7849041ad9..7d4d7565e8ee3 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -925,6 +925,8 @@ static int damos_va_stat_pmd_entry(pmd_t *pmd, unsigned long addr, return 0; for (; addr < next; pte += nr, addr += nr * PAGE_SIZE) { + unsigned long page_idx; + nr = 1; ptent = ptep_get(pte); @@ -938,7 +940,8 @@ static int damos_va_stat_pmd_entry(pmd_t *pmd, unsigned long addr, if (!damos_va_filter_out(s, folio, vma, addr, pte, NULL)) *sz_filter_passed += folio_size(folio); - nr = folio_nr_pages(folio); + page_idx = folio_page_idx(folio, pte_page(ptent)); + nr = folio_nr_pages(folio) - page_idx; s->last_applied = folio; } pte_unmap_unlock(start_pte, ptl); -- 2.53.0