[PATCH v3 2/4] mm/gup: clean up follow_pfn_pte() slightly

John Hubbard
2022-02-03T09:33:12Z

Regardless of any FOLL_* flags, get_user_pages() and its variants should
handle PFN-only entries by stopping early, if the caller expected
**pages to be filled in.

This makes for a more reliable API, as compared to the previous approach
of skipping over such entries (and thus leaving them silently
unwritten).

Cc: Peter Xu <peterx@redhat.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
mm/gup.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 65575ae3602f..cad3f28492e3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -439,10 +439,6 @@ static struct page *no_page_table(struct vm_area_struct *vma,
static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, unsigned int flags)
{
- /* No page to get reference */
- if (flags & (FOLL_GET | FOLL_PIN))
- return -EFAULT;
-
if (flags & FOLL_TOUCH) {
pte_t entry = *pte;

@@ -1180,8 +1176,13 @@ static long __get_user_pages(struct mm_struct *mm,
} else if (PTR_ERR(page) == -EEXIST) {
/*
* Proper page table entry exists, but no corresponding
- * struct page.
+ * struct page. If the caller expects **pages to be
+ * filled in, bail out now, because that can't be done
+ * for this page.
*/
+ if (pages)
+ goto out;
+
goto next_page;
} else if (IS_ERR(page)) {
ret = PTR_ERR(page);
--
2.35.1