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From:   Peter Xu <peterx@redhat.com>
To:     linux-kernel@vger.kernel.org, linux-mm@kvack.org
Cc:     Axel Rasmussen <axelrasmussen@google.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Jerome Glisse <jglisse@redhat.com>,
        "Kirill A . Shutemov" <kirill@shutemov.name>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Alistair Popple <apopple@nvidia.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>, peterx@redhat.com,
        Andrea Arcangeli <aarcange@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Tiberiu Georgescu <tiberiu.georgescu@nutanix.com>,
        Hugh Dickins <hughd@google.com>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>
Subject: [PATCH v5 14/26] shmem/userfaultfd: Pass over uffd-wp special swap pte when fork()
Date:   Thu, 15 Jul 2021 16:16:10 -0400
Message-Id: <20210715201610.211610-1-peterx@redhat.com>
In-Reply-To: <20210715201422.211004-1-peterx@redhat.com>
References: <20210715201422.211004-1-peterx@redhat.com>
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It should be handled similarly like other uffd-wp wr-protected ptes: we should
pass it over when the dst_vma has VM_UFFD_WP armed, otherwise drop it.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/memory.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 223781f115e9..af91bee934c7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -776,8 +776,21 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	unsigned long vm_flags = dst_vma->vm_flags;
 	pte_t pte = *src_pte;
 	struct page *page;
-	swp_entry_t entry = pte_to_swp_entry(pte);
+	swp_entry_t entry;
+
+	if (unlikely(is_swap_special_pte(pte))) {
+		/*
+		 * uffd-wp special swap pte is the only possibility for now.
+		 * If dst vma is registered with uffd-wp, copy it over.
+		 * Otherwise, ignore this pte as if it's a none pte would work.
+		 */
+		WARN_ON_ONCE(!pte_swp_uffd_wp_special(pte));
+		if (userfaultfd_wp(dst_vma))
+			set_pte_at(dst_mm, addr, dst_pte, pte);
+		return 0;
+	}
 
+	entry = pte_to_swp_entry(pte);
 	if (likely(!non_swap_entry(entry))) {
 		if (swap_duplicate(entry) < 0)
 			return -EIO;
-- 
2.31.1