mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register

Ralph observes that hmm_range_register() can only be called by a driver
while a mirror is registered. Make this clear in the API by passing in the
mirror structure as a parameter.

This also simplifies understanding the lifetime model for struct hmm, as
the hmm pointer must be valid as part of a registered mirror so all we
need in hmm_register_range() is a simple kref_get.

Suggested-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>

1 files changed, 4 insertions, 9 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index f6956d78e3cb..22a97ada108b 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -914,13 +914,13 @@ static void hmm_pfns_clear(struct hmm_range *range,
  * Track updates to the CPU page table see include/linux/hmm.h
  */
 int hmm_range_register(struct hmm_range *range,
-		       struct mm_struct *mm,
+		       struct hmm_mirror *mirror,
 		       unsigned long start,
 		       unsigned long end,
 		       unsigned page_shift)
 {
 	unsigned long mask = ((1UL << page_shift) - 1UL);
-	struct hmm *hmm;
+	struct hmm *hmm = mirror->hmm;
 
 	range->valid = false;
 	range->hmm = NULL;
@@ -934,20 +934,15 @@ int hmm_range_register(struct hmm_range *range,
 	range->start = start;
 	range->end = end;
 
-	hmm = hmm_get_or_create(mm);
-	if (!hmm)
-		return -EFAULT;
-
 	/* Check if hmm_mm_destroy() was call. */
-	if (hmm->mm == NULL || hmm->dead) {
-		hmm_put(hmm);
+	if (hmm->mm == NULL || hmm->dead)
 		return -EFAULT;
-	}
 
 	/* Initialize range to track CPU page table updates. */
 	mutex_lock(&hmm->lock);
 
 	range->hmm = hmm;
+	kref_get(&hmm->kref);
 	list_add_rcu(&range->list, &hmm->ranges);
 
 	/*