+ mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch added to mm-unstable branch

+ mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/gup.c: don't pass gup_flags to check_and_migrate_movable_pages()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Alistair Popple <apopple@nvidia.com>
Subject: mm/gup.c: don't pass gup_flags to check_and_migrate_movable_pages()
Date: Wed, 24 Aug 2022 15:09:51 +1000

gup_flags is passed to check_and_migrate_movable_pages() so that it can
call either put_page() or unpin_user_page() to drop the page reference. 
However check_and_migrate_movable_pages() is only called for
FOLL_LONGTERM, which implies FOLL_PIN so there is no need to pass
gup_flags.

Link: https://lkml.kernel.org/r/d611c65a9008ff55887307df457c6c2220ad6163.1661317396.git-series.apopple@nvidia.com
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Alex Sierra <alex.sierra@amd.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Felix Kuehling <felix.kuehling@amd.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Shigeru Yoshida <syoshida@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/gup.c |   23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

--- a/mm/gup.c~mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages
+++ a/mm/gup.c
@@ -1910,8 +1910,7 @@ struct page *get_dump_page(unsigned long
  * migration failure.
  */
 static long check_and_migrate_movable_pages(unsigned long nr_pages,
-					    struct page **pages,
-					    unsigned int gup_flags)
+					    struct page **pages)
 {
 	unsigned long i;
 	struct folio *prev_folio = NULL;
@@ -1944,10 +1943,8 @@ static long check_and_migrate_movable_pa
 			 * Migration will fail if the page is pinned, so convert
 			 * the pin on the source page to a normal reference.
 			 */
-			if (gup_flags & FOLL_PIN) {
-				get_page(&folio->page);
-				unpin_user_page(&folio->page);
-			}
+			get_page(&folio->page);
+			unpin_user_page(&folio->page);
 
 			if (migrate_device_coherent_page(&folio->page)) {
 				ret = -EBUSY;
@@ -2000,10 +1997,7 @@ static long check_and_migrate_movable_pa
 		if (!pages[i])
 			continue;
 
-		if (gup_flags & FOLL_PIN)
-			unpin_user_page(pages[i]);
-		else
-			put_page(pages[i]);
+		unpin_user_page(pages[i]);
 	}
 
 	if (!list_empty(&movable_page_list)) {
@@ -2026,8 +2020,7 @@ static long check_and_migrate_movable_pa
 }
 #else
 static long check_and_migrate_movable_pages(unsigned long nr_pages,
-					    struct page **pages,
-					    unsigned int gup_flags)
+					    struct page **pages)
 {
 	return 0;
 }
@@ -2050,6 +2043,9 @@ static long __gup_longterm_locked(struct
 	if (!(gup_flags & FOLL_LONGTERM))
 		return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
 					       NULL, gup_flags);
+	/* check_and_migrate_movable_pages() assumes pages have been pinned. */
+	if (WARN_ON(!(gup_flags & FOLL_PIN)))
+		return -EINVAL;
 	flags = memalloc_pin_save();
 	do {
 		nr_pinned_pages = __get_user_pages_locked(mm, start, nr_pages,
@@ -2057,8 +2053,7 @@ static long __gup_longterm_locked(struct
 							  gup_flags);
 		if (nr_pinned_pages <= 0)
 			break;
-		rc = check_and_migrate_movable_pages(nr_pinned_pages, pages,
-						     gup_flags);
+		rc = check_and_migrate_movable_pages(nr_pinned_pages, pages);
 	} while (rc == -EAGAIN);
 	memalloc_pin_restore(flags);
 
_

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

mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch
mm-gupc-simplify-and-fix-check_and_migrate_movable_pages-return-codes.patch
selftests-hmm-tests-add-test-for-dirty-bits.patch
mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch
mm-gupc-refactor-check_and_migrate_movable_pages.patch