Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu,  5 Jan 2023 10:18:14 +0000
In-Reply-To: <20230105101844.1893104-1-jthoughton@google.com>
Mime-Version: 1.0
References: <20230105101844.1893104-1-jthoughton@google.com>
Message-ID: <20230105101844.1893104-17-jthoughton@google.com>
Subject: [PATCH 16/46] hugetlbfs: do a full walk to check if vma maps a page
From:   James Houghton <jthoughton@google.com>
To:     Mike Kravetz <mike.kravetz@oracle.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Peter Xu <peterx@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        David Rientjes <rientjes@google.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mina Almasry <almasrymina@google.com>,
        "Zach O'Keefe" <zokeefe@google.com>,
        Manish Mishra <manish.mishra@nutanix.com>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Yang Shi <shy828301@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        James Houghton <jthoughton@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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@google.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