[PATCH v3 18/27] hugetlb/userfaultfd: Hook page faults for uffd write protection

Peter Xu
2021-05-27T20:23:20Z

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 69a4b551c157..4cbbffd50080 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4980,6 +4980,25 @@ 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
--
2.31.1