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From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
CC: Al Viro <viro@zeniv.linux.org.uk>, Alex Williamson
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Subject: [PATCH v2 06/19] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call
Date: Mon, 25 Nov 2019 15:10:22 -0800
Message-ID: <20191125231035.1539120-7-jhubbard@nvidia.com>
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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.

Tested-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/vfio/vfio_iommu_type1.c | 30 +++++-------------------------
 1 file changed, 5 insertions(+), 25 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type=
1.c
index 2ada8e6cdb88..b800fc9a0251 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -322,7 +322,6 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned=
 long vaddr,
 {
 	struct page *page[1];
 	struct vm_area_struct *vma;
-	struct vm_area_struct *vmas[1];
 	unsigned int flags =3D 0;
 	int ret;
=20
@@ -330,33 +329,14 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsign=
ed long vaddr,
 		flags |=3D FOLL_WRITE;
=20
 	down_read(&mm->mmap_sem);
-	if (mm =3D=3D current->mm) {
-		ret =3D get_user_pages(vaddr, 1, flags | FOLL_LONGTERM, page,
-				     vmas);
-	} else {
-		ret =3D 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 =3D -EOPNOTSUPP;
-			put_page(page[0]);
-		}
-	}
-	up_read(&mm->mmap_sem);
-
+	ret =3D get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM,
+				    page, NULL, NULL);
 	if (ret =3D=3D 1) {
 		*pfn =3D page_to_pfn(page[0]);
-		return 0;
+		ret =3D 0;
+		goto done;
 	}
=20
-	down_read(&mm->mmap_sem);
-
 	vaddr =3D untagged_addr(vaddr);
=20
 	vma =3D find_vma_intersection(mm, vaddr, vaddr + 1);
@@ -366,7 +346,7 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned=
 long vaddr,
 		if (is_invalid_reserved_pfn(*pfn))
 			ret =3D 0;
 	}
-
+done:
 	up_read(&mm->mmap_sem);
 	return ret;
 }
--=20
2.24.0