[15/23] hugetlb/userfaultfd: Hook page faults for uffd write protection

Commit Message

Peter Xu March 23, 2021, 12:49 a.m. UTC

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.

Signed-off-by: Peter Xu <[e-mail]>
---
 mm/hugetlb.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

Comments

Mike Kravetz April 21, 2021, 10:02 p.m. UTC | #1

On 3/22/21 5:49 PM, Peter Xu wrote:
> 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.
> 
> Signed-off-by: Peter Xu <[e-mail]>
> ---
>  mm/hugetlb.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)

That is pretty straight forward,

Reviewed-by: Mike Kravetz <[e-mail]>

Patch

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 56b78a206913..def2c7ddf3ae 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4643,6 +4643,25 @@  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_pte_wp(vma, 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