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.william...@redhat.com>
Acked-by: Alex Williamson <alex.william...@redhat.com>
Reviewed-by: Jason Gunthorpe <j...@mellanox.com>
Reviewed-by: Ira Weiny <ira.we...@intel.com>
Suggested-by: Jason Gunthorpe <j...@ziepe.ca>
Cc: Dan Williams <dan.j.willi...@intel.com>
Cc: Jerome Glisse <jgli...@redhat.com>
Signed-off-by: John Hubbard <jhubb...@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;
 }
-- 
2.24.0

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