mm/migrate: fix migrate_pgmap_owner w/o CONFIG_MMU_NOTIFIER

On x86_64, when CONFIG_MMU_NOTIFIER is not set/enabled, there is a
compiler error:

   mm/migrate.c: In function 'migrate_vma_collect':
   mm/migrate.c:2481:7: error: 'struct mmu_notifier_range' has no member named 'migrate_pgmap_owner'
     range.migrate_pgmap_owner = migrate->pgmap_owner;
          ^

Fixes: 998427b3 ("mm/notifier: add migration invalidation type")
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: "Jason Gunthorpe" <jgg@mellanox.com>
Link: http://lkml.kernel.org/r/20200806193353.7124-1-rcampbell@nvidia.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmu_notifier.h

@@ -521,6 +521,16 @@ static inline void mmu_notifier_range_init(struct mmu_notifier_range *range,
 	range->flags = flags;
 }
 
+static inline void mmu_notifier_range_init_migrate(
+			struct mmu_notifier_range *range, unsigned int flags,
+			struct vm_area_struct *vma, struct mm_struct *mm,
+			unsigned long start, unsigned long end, void *pgmap)
+{
+	mmu_notifier_range_init(range, MMU_NOTIFY_MIGRATE, flags, vma, mm,
+				start, end);
+	range->migrate_pgmap_owner = pgmap;
+}
+
 #define ptep_clear_flush_young_notify(__vma, __address, __ptep)		\
 ({									\
 	int __young;							\
@@ -645,6 +655,9 @@ static inline void _mmu_notifier_range_init(struct mmu_notifier_range *range,
 
 #define mmu_notifier_range_init(range,event,flags,vma,mm,start,end)  \
 	_mmu_notifier_range_init(range, start, end)
+#define mmu_notifier_range_init_migrate(range, flags, vma, mm, start, end, \
+					pgmap) \
+	_mmu_notifier_range_init(range, start, end)
 
 static inline bool
 mmu_notifier_range_blockable(const struct mmu_notifier_range *range)

mm/migrate.c

@@ -2386,9 +2386,9 @@ static void migrate_vma_collect(struct migrate_vma *migrate)
 	 * that the registered device driver can skip invalidating device
 	 * private page mappings that won't be migrated.
 	 */
-	mmu_notifier_range_init(&range, MMU_NOTIFY_MIGRATE, 0, migrate->vma,
-			migrate->vma->vm_mm, migrate->start, migrate->end);
-	range.migrate_pgmap_owner = migrate->pgmap_owner;
+	mmu_notifier_range_init_migrate(&range, 0, migrate->vma,
+		migrate->vma->vm_mm, migrate->start, migrate->end,
+		migrate->pgmap_owner);
 	mmu_notifier_invalidate_range_start(&range);
 
 	walk_page_range(migrate->vma->vm_mm, migrate->start, migrate->end,