[PATCH v6 12/23] mm/hugetlb: Hook page faults for uffd write protection

From: Peter Xu <peterx@redhat.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Nadav Amit <nadav.amit@gmail.com>,
	peterx@redhat.com, Alistair Popple <apopple@nvidia.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Matthew Wilcox <willy@infradead.org>,
	Jerome Glisse <jglisse@redhat.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	David Hildenbrand <david@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Hugh Dickins <hughd@google.com>
Subject: [PATCH v6 12/23] mm/hugetlb: Hook page faults for uffd write protection
Date: Mon, 15 Nov 2021 16:01:32 +0800	[thread overview]
Message-ID: <20211115080132.74754-1-peterx@redhat.com> (raw)
In-Reply-To: <20211115075522.73795-1-peterx@redhat.com>

Hook up hugetlbfs_fault() with the capability to handle userfaultfd-wp faults.

We do this slightly earlier than hugetlb_cow() so that we can avoid taking some
extra locks that we definitely don't need.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/hugetlb.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e09159c957e3..3a10274b2e39 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5658,6 +5658,25 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (unlikely(!pte_same(entry, huge_ptep_get(ptep))))
 		goto out_ptl;
 
+	/* Handle userfault-wp first, before trying to lock more pages */
+	if (userfaultfd_wp(vma) && huge_pte_uffd_wp(huge_ptep_get(ptep)) &&
+	    (flags & FAULT_FLAG_WRITE) && !huge_pte_write(entry)) {
+		struct vm_fault vmf = {
+			.vma = vma,
+			.address = haddr,
+			.flags = flags,
+		};
+
+		spin_unlock(ptl);
+		if (pagecache_page) {
+			unlock_page(pagecache_page);
+			put_page(pagecache_page);
+		}
+		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+		i_mmap_unlock_read(mapping);
+		return handle_userfault(&vmf, VM_UFFD_WP);
+	}
+
 	/*
 	 * hugetlb_cow() requires page locks of pte_page(entry) and
 	 * pagecache_page, so here we need take the former one
-- 
2.32.0

