[042/118] vfio, mm: pin_user_pages (FOLL_PIN) and put_user_page() conversion

Commit Message

Andrew Morton Jan. 31, 2020, 6:13 a.m. UTC

From: John Hubbard <[e-mail]>
Subject: vfio, mm: pin_user_pages (FOLL_PIN) and put_user_page() conversion

1. Change vfio from get_user_pages_remote(), to
   pin_user_pages_remote().

2. Because all FOLL_PIN-acquired pages must be released via
   put_user_page(), also convert the put_page() call over to
   put_user_pages_dirty_lock().

Note that this effectively changes the code's behavior in
vfio_iommu_type1.c: put_pfn(): it now ultimately calls
set_page_dirty_lock(), instead of set_page_dirty().  This is probably more
accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

[1] https://lore.kernel.org/r/[e-mail]

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Tested-by: Alex Williamson <[e-mail]>
Acked-by: Alex Williamson <[e-mail]>
Cc: Aneesh Kumar K.V <[e-mail]>
Cc: Björn Töpel <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Hans Verkuil <[e-mail]>
Cc: Ira Weiny <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Jerome Glisse <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Leon Romanovsky <[e-mail]>
Cc: Mauro Carvalho Chehab <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 drivers/vfio/vfio_iommu_type1.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Patch

--- a/drivers/vfio/vfio_iommu_type1.c~vfio-mm-pin_user_pages-foll_pin-and-put_user_page-conversion
+++ a/drivers/vfio/vfio_iommu_type1.c
@@ -309,9 +309,8 @@  static int put_pfn(unsigned long pfn, in
 {
 	if (!is_invalid_reserved_pfn(pfn)) {
 		struct page *page = pfn_to_page(pfn);
-		if (prot & IOMMU_WRITE)
-			SetPageDirty(page);
-		put_page(page);
+
+		put_user_pages_dirty_lock(&page, 1, prot & IOMMU_WRITE);
 		return 1;
 	}
 	return 0;
@@ -329,7 +328,7 @@  static int vaddr_get_pfn(struct mm_struc
 		flags |= FOLL_WRITE;
 
 	down_read(&mm->mmap_sem);
-	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
+	ret = pin_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
 				    page, NULL, NULL);
 	if (ret == 1) {
 		*pfn = page_to_pfn(page[0]);