drm/radeon: Refuse to migrate a prime BO to VRAM. (v2)

BOs shared via dma-buf, either imported or exported, cannot sensibly be migrated to VRAM
without breaking the dma-buf sharing. Refuse userspace requests to migrate to VRAM,
ensure such BOs are not migrated during command submission, and refuse to pin them
to VRAM.

v2: Don't pin BOs in GTT. Instead, refuse to migrate BOs to VRAM.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christopher James Halse Rogers <christopher.halse.rogers@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_cs.c

@@ -164,6 +164,16 @@ static int radeon_cs_parser_relocs(struct radeon_cs_parser *p)
 			p->relocs[i].allowed_domains = domain;
 		}
 
+		/* Objects shared as dma-bufs cannot be moved to VRAM */
+		if (p->relocs[i].robj->prime_shared_count) {
+			p->relocs[i].allowed_domains &= ~RADEON_GEM_DOMAIN_VRAM;
+			if (!p->relocs[i].allowed_domains) {
+				DRM_ERROR("BO associated with dma-buf cannot "
+					  "be moved to VRAM\n");
+				return -EINVAL;
+			}
+		}
+
 		p->relocs[i].tv.bo = &p->relocs[i].robj->tbo;
 		p->relocs[i].tv.shared = !r->write_domain;
 

drivers/gpu/drm/radeon/radeon_gem.c

@@ -120,6 +120,10 @@ static int radeon_gem_set_domain(struct drm_gem_object *gobj,
 			return r;
 		}
 	}
+	if (domain == RADEON_GEM_DOMAIN_VRAM && robj->prime_shared_count) {
+		/* A BO that is associated with a dma-buf cannot be sensibly migrated to VRAM */
+		return -EINVAL;
+	}
 	return 0;
 }
 

drivers/gpu/drm/radeon/radeon_object.c

@@ -352,6 +352,11 @@ int radeon_bo_pin_restricted(struct radeon_bo *bo, u32 domain, u64 max_offset,
 
 		return 0;
 	}
+	if (bo->prime_shared_count && domain == RADEON_GEM_DOMAIN_VRAM) {
+		/* A BO shared as a dma-buf cannot be sensibly migrated to VRAM */
+		return -EINVAL;
+	}
+
 	radeon_ttm_placement_from_domain(bo, domain);
 	for (i = 0; i < bo->placement.num_placement; i++) {
 		/* force to pin into visible video ram */