linux-kernel - [PATCH 16/46] hugetlbfs: do a full walk to check if vma maps a page

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Message-ID: <20230105101844.1893104-17-jthoughton@google.com>
Date:   Thu,  5 Jan 2023 10:18:14 +0000
From:   James Houghton <jthoughton@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        "Zach O'Keefe" <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        James Houghton <jthoughton@...gle.com>
Subject: [PATCH 16/46] hugetlbfs: do a full walk to check if vma maps a page

Because it is safe to do so, we can do a full high-granularity page
table walk to check if the page is mapped.

If it were not safe to do so, we could bail out early in the case of a
high-granularity mapped PTE, indicating that the page could have been
mapped.

Signed-off-by: James Houghton <jthoughton@...gle.com>
---
 fs/hugetlbfs/inode.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 48f1a8ad2243..d34ce79da595 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -386,17 +386,24 @@ static void hugetlb_delete_from_page_cache(struct folio *folio)
 static bool hugetlb_vma_maps_page(struct vm_area_struct *vma,
 				unsigned long addr, struct page *page)
 {
-	pte_t *ptep, pte;
+	pte_t pte;
+	struct hugetlb_pte hpte;
 
-	ptep = hugetlb_walk(vma, addr, huge_page_size(hstate_vma(vma)));
-	if (!ptep)
+	if (hugetlb_full_walk(&hpte, vma, addr))
 		return false;
 
-	pte = huge_ptep_get(ptep);
+	pte = huge_ptep_get(hpte.ptep);
 	if (huge_pte_none(pte) || !pte_present(pte))
 		return false;
 
-	if (pte_page(pte) == page)
+	if (unlikely(!hugetlb_pte_present_leaf(&hpte, pte)))
+		/*
+		 * We raced with someone splitting us, and the only case
+		 * where this is impossible is when the pte was none.
+		 */
+		return false;
+
+	if (compound_head(pte_page(pte)) == page)
 		return true;
 
 	return false;
-- 
2.39.0.314.g84b9a713c41-goog