mm/hmm: improve and rename hmm_vma_get_pfns() to hmm_range_snapshot()

Rename for consistency between code, comments and documentation.  Also
improves the comments on all the possible returns values.  Improve the
function by returning the number of populated entries in pfns array.

Link: http://lkml.kernel.org/r/20190129165428.3931-4-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 10 insertions, 13 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index 510f95e3b4e8..c718329dfb6e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -706,23 +706,19 @@ static void hmm_pfns_special(struct hmm_range *range)
 }
 
 /*
- * hmm_vma_get_pfns() - snapshot CPU page table for a range of virtual addresses
- * @range: range being snapshotted
+ * hmm_range_snapshot() - snapshot CPU page table for a range
+ * @range: range
  * Returns: -EINVAL if invalid argument, -ENOMEM out of memory, -EPERM invalid
- *          vma permission, 0 success
+ *          permission (for instance asking for write and range is read only),
+ *          -EAGAIN if you need to retry, -EFAULT invalid (ie either no valid
+ *          vma or it is illegal to access that range), number of valid pages
+ *          in range->pfns[] (from range start address).
  *
  * This snapshots the CPU page table for a range of virtual addresses. Snapshot
  * validity is tracked by range struct. See hmm_vma_range_done() for further
  * information.
- *
- * The range struct is initialized here. It tracks the CPU page table, but only
- * if the function returns success (0), in which case the caller must then call
- * hmm_vma_range_done() to stop CPU page table update tracking on this range.
- *
- * NOT CALLING hmm_vma_range_done() IF FUNCTION RETURNS 0 WILL LEAD TO SERIOUS
- * MEMORY CORRUPTION ! YOU HAVE BEEN WARNED !
  */
-int hmm_vma_get_pfns(struct hmm_range *range)
+long hmm_range_snapshot(struct hmm_range *range)
 {
 	struct vm_area_struct *vma = range->vma;
 	struct hmm_vma_walk hmm_vma_walk;
@@ -776,6 +772,7 @@ int hmm_vma_get_pfns(struct hmm_range *range)
 	hmm_vma_walk.fault = false;
 	hmm_vma_walk.range = range;
 	mm_walk.private = &hmm_vma_walk;
+	hmm_vma_walk.last = range->start;
 
 	mm_walk.vma = vma;
 	mm_walk.mm = vma->vm_mm;
@@ -792,9 +789,9 @@ int hmm_vma_get_pfns(struct hmm_range *range)
 	 * function return 0).
 	 */
 	range->hmm = hmm;
-	return 0;
+	return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
 }
-EXPORT_SYMBOL(hmm_vma_get_pfns);
+EXPORT_SYMBOL(hmm_range_snapshot);
 
 /*
  * hmm_vma_range_done() - stop tracking change to CPU page table over a range