linux-kernel - [PATCH 2/2] mm: pvmw: check possible huge PMD map by transhuge_vma

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Date:   Thu, 12 May 2022 10:45:51 -0700
From:   Yang Shi <shy828301@...il.com>
To:     willy@...radead.org, songmuchun@...edance.com,
        akpm@...ux-foundation.org
Cc:     shy828301@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] mm: pvmw: check possible huge PMD map by transhuge_vma_suitable()

IIUC PVMW checks if the vma is possibly huge PMD mapped by
transparent_hugepage_active() and "pvmw->nr_pages >= HPAGE_PMD_NR".

Actually pvmw->nr_pages is returned by compound_nr() or
folio_nr_pages(), so the page should be THP as long as "pvmw->nr_pages
>= HPAGE_PMD_NR".  And it is guaranteed THP is allocated for valid VMA
in the first place.  But it may be not PMD mapped if the VMA is file
VMA and it is not properly aligned.  The transhuge_vma_suitable()
is used to do such check, so replace transparent_hugepage_active() to
it, which is too heavy and overkilling.

Fixes: 2aff7a4755be ("mm: Convert page_vma_mapped_walk to work on PFNs")
Signed-off-by: Yang Shi <shy828301@...il.com>
---
 mm/page_vma_mapped.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c
index c10f839fc410..2634565be175 100644
--- a/mm/page_vma_mapped.c
+++ b/mm/page_vma_mapped.c
@@ -237,13 +237,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
 			spin_unlock(pvmw->ptl);
 			pvmw->ptl = NULL;
 		} else if (!pmd_present(pmde)) {
+			unsigned long haddr = pvmw->address & HPAGE_PMD_MASK;
 			/*
 			 * If PVMW_SYNC, take and drop THP pmd lock so that we
 			 * cannot return prematurely, while zap_huge_pmd() has
 			 * cleared *pmd but not decremented compound_mapcount().
 			 */
 			if ((pvmw->flags & PVMW_SYNC) &&
-			    transparent_hugepage_active(vma) &&
+			    transhuge_vma_suitable(vma, haddr) &&
 			    (pvmw->nr_pages >= HPAGE_PMD_NR)) {
 				spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
 
-- 
2.26.3