[030/118] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call

Commit Message

Andrew Morton Jan. 31, 2020, 6:12 a.m. UTC

From: John Hubbard <[e-mail]>
Subject: vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call

Update VFIO to take advantage of the recently loosened restriction on
FOLL_LONGTERM with get_user_pages_remote().  Also, now it is possible to
fix a bug: the VFIO caller is logically a FOLL_LONGTERM user, but it
wasn't setting FOLL_LONGTERM.

Also, remove an unnessary pair of calls that were releasing and
reacquiring the mmap_sem.  There is no need to avoid holding mmap_sem just
in order to call page_to_pfn().

Also, now that the the DAX check ("if a VMA is DAX, don't allow long term
pinning") is in the internals of get_user_pages_remote() and
__gup_longterm_locked(), there's no need for it at the VFIO call site.  So
remove it.

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]>
Reviewed-by: Jason Gunthorpe <[e-mail]>
Reviewed-by: Ira Weiny <[e-mail]>
Suggested-by: Jason Gunthorpe <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Jerome Glisse <[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: Hans Verkuil <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Jens Axboe <[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 |   30 +++++-------------------------
 1 file changed, 5 insertions(+), 25 deletions(-)

Patch

--- a/drivers/vfio/vfio_iommu_type1.c~vfio-fix-foll_longterm-use-simplify-get_user_pages_remote-call
+++ a/drivers/vfio/vfio_iommu_type1.c
@@ -322,7 +322,6 @@  static int vaddr_get_pfn(struct mm_struc
 {
 	struct page *page[1];
 	struct vm_area_struct *vma;
-	struct vm_area_struct *vmas[1];
 	unsigned int flags = 0;
 	int ret;
 
@@ -330,33 +329,14 @@  static int vaddr_get_pfn(struct mm_struc
 		flags |= FOLL_WRITE;
 
 	down_read(&mm->mmap_sem);
-	if (mm == current->mm) {
-		ret = get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
-				     vmas);
-	} else {
-		ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags, page,
-					    vmas, NULL);
-		/*
-		 * The lifetime of a vaddr_get_pfn() page pin is
-		 * userspace-controlled. In the fs-dax case this could
-		 * lead to indefinite stalls in filesystem operations.
-		 * Disallow attempts to pin fs-dax pages via this
-		 * interface.
-		 */
-		if (ret > 0 && vma_is_fsdax(vmas[0])) {
-			ret = -EOPNOTSUPP;
-			put_page(page[0]);
-		}
-	}
-	up_read(&mm->mmap_sem);
-
+	ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
+				    page, NULL, NULL);
 	if (ret == 1) {
 		*pfn = page_to_pfn(page[0]);
-		return 0;
+		ret = 0;
+		goto done;
 	}
 
-	down_read(&mm->mmap_sem);
-
 	vaddr = untagged_addr(vaddr);
 
 	vma = find_vma_intersection(mm, vaddr, vaddr + 1);
@@ -366,7 +346,7 @@  static int vaddr_get_pfn(struct mm_struc
 		if (is_invalid_reserved_pfn(*pfn))
 			ret = 0;
 	}
-
+done:
 	up_read(&mm->mmap_sem);
 	return ret;
 }