[PATCH v11 07/25] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call

John Hubbard
2019-12-16T22:28:07Z

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_type1.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 = 0;
int ret;

@@ -330,33 +329,14 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
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_struct *mm, unsigned long vaddr,
if (is_invalid_reserved_pfn(*pfn))
ret = 0;
}
-
+done:
up_read(&mm->mmap_sem);
return ret;
}
--
2.24.1