memremap: add an owner field to struct dev_pagemap

Add a new opaque owner field to struct dev_pagemap, which will allow the
hmm and migrate_vma code to identify who owns ZONE_DEVICE memory, and
refuse to work on mappings not owned by the calling entity.

Link: https://lore.kernel.org/r/20200316193216.920734-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Tested-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

arch/powerpc/kvm/book3s_hv_uvmem.c

@@ -779,6 +779,8 @@ int kvmppc_uvmem_init(void)
 	kvmppc_uvmem_pgmap.type = MEMORY_DEVICE_PRIVATE;
 	kvmppc_uvmem_pgmap.res = *res;
 	kvmppc_uvmem_pgmap.ops = &kvmppc_uvmem_ops;
+	/* just one global instance: */
+	kvmppc_uvmem_pgmap.owner = &kvmppc_uvmem_pgmap;
 	addr = memremap_pages(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
 	if (IS_ERR(addr)) {
 		ret = PTR_ERR(addr);

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -526,6 +526,7 @@ nouveau_dmem_init(struct nouveau_drm *drm)
 	drm->dmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
 	drm->dmem->pagemap.res = *res;
 	drm->dmem->pagemap.ops = &nouveau_dmem_pagemap_ops;
+	drm->dmem->pagemap.owner = drm->dev;
 	if (IS_ERR(devm_memremap_pages(device, &drm->dmem->pagemap)))
 		goto out_free;
 

include/linux/memremap.h

@@ -103,6 +103,9 @@ struct dev_pagemap_ops {
  * @type: memory type: see MEMORY_* in memory_hotplug.h
  * @flags: PGMAP_* flags to specify defailed behavior
  * @ops: method table
+ * @owner: an opaque pointer identifying the entity that manages this
+ *	instance.  Used by various helpers to make sure that no
+ *	foreign ZONE_DEVICE memory is accessed.
  */
 struct dev_pagemap {
 	struct vmem_altmap altmap;
@@ -113,6 +116,7 @@ struct dev_pagemap {
 	enum memory_type type;
 	unsigned int flags;
 	const struct dev_pagemap_ops *ops;
+	void *owner;
 };
 
 static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)

mm/memremap.c

@@ -181,6 +181,10 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
 			WARN(1, "Missing migrate_to_ram method\n");
 			return ERR_PTR(-EINVAL);
 		}
+		if (!pgmap->owner) {
+			WARN(1, "Missing owner\n");
+			return ERR_PTR(-EINVAL);
+		}
 		break;
 	case MEMORY_DEVICE_FS_DAX:
 		if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||