+ mm-gup-clean-up-follow_pfn_pte-slightly.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/gup: clean up follow_pfn_pte() slightly
has been added to the -mm tree.  Its filename is
     mm-gup-clean-up-follow_pfn_pte-slightly.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-gup-clean-up-follow_pfn_pte-slightly.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-gup-clean-up-follow_pfn_pte-slightly.patch

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------------------------------------------------------
From: John Hubbard <jhubbard@nvidia.com>
Subject: mm/gup: clean up follow_pfn_pte() slightly

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).

Link: https://lkml.kernel.org/r/20220201101108.306062-3-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/gup.c |   12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

--- a/mm/gup.c~mm-gup-clean-up-follow_pfn_pte-slightly
+++ a/mm/gup.c
@@ -439,10 +439,6 @@ static struct page *no_page_table(struct
 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 +1176,14 @@ retry:
 		} 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) {
+				page = ERR_PTR(-EFAULT);
+				goto out;
+			}
 			goto next_page;
 		} else if (IS_ERR(page)) {
 			ret = PTR_ERR(page);
_

Patches currently in -mm which might be from jhubbard@nvidia.com are

mm-gup-clean-up-follow_pfn_pte-slightly.patch
mm-gup-remove-unused-pin_user_pages_locked.patch
mm-gup-remove-get_user_pages_locked.patch