drm/gpusvm, drm/xe: Allow mixed mappings for userptr

Compute kernels often issue memory copies immediately after completion.
If the memory being copied is an SVM pointer that was faulted into the
device and then bound via userptr, it is undesirable to move that
memory. Worse, if userptr is mixed between system and device memory, the
bind operation may be rejected.

Xe already has the necessary plumbing to support userptr with mixed
mappings. This update modifies GPUSVM's get_pages to correctly locate
pages in such mixed mapping scenarios.

v2:
- Rebase (Thomas Hellström)
v3:
- Remove Fixes tag.
v4:
- Break out from series since the other patch was merged.
- Update patch subject, ensure dri-devel and Maarten are CC'd.

Cc: Maarten Lankhorst <[e-mail]>
Cc: [e-mail]
Signed-off-by: Matthew Brost <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]>
Reviewed-by: Matthew Auld <[e-mail]>
Reviewed-by: Himal Prasad Ghimiray <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Acked-by: Maarten Lankhorst <[e-mail]>
Signed-off-by: Thomas Hellström <[e-mail]>

drivers/gpu/drm/drm_gpusvm.c

···
 		order = drm_gpusvm_hmm_pfn_to_order(pfns[i], i, npages);
 		if (is_device_private_page(page) ||
 		    is_device_coherent_page(page)) {
-			if (zdd != page->zone_device_data && i > 0) {
+			if (!ctx->allow_mixed &&
+			    zdd != page->zone_device_data && i > 0) {
 				err = -EOPNOTSUPP;
 				goto err_unmap;
 			}
···
 		} else {
 			dma_addr_t addr;
 
-			if (is_zone_device_page(page) || pagemap) {
+			if (is_zone_device_page(page) ||
+			    (pagemap && !ctx->allow_mixed)) {
 				err = -EOPNOTSUPP;
 				goto err_unmap;
 			}

drivers/gpu/drm/xe/xe_userptr.c

···
  * Copyright © 2025 Intel Corporation
  */
 
+#include "xe_svm.h"
 #include "xe_userptr.h"
 
 #include <linux/mm.h>
···
 	struct xe_device *xe = vm->xe;
 	struct drm_gpusvm_ctx ctx = {
 		.read_only = xe_vma_read_only(vma),
-		.device_private_page_owner = NULL,
+		.device_private_page_owner = xe_svm_devm_owner(xe),
+		.allow_mixed = true,
 	};
 
 	lockdep_assert_held(&vm->lock);

include/drm/drm_gpusvm.h

···
  * @read_only: operating on read-only memory
  * @devmem_possible: possible to use device memory
  * @devmem_only: use only device memory
+ * @allow_mixed: Allow mixed mappings in get pages. Mixing between system and
+ *               single dpagemap is supported, mixing between multiple dpagemap
+ *               is unsupported.
  *
  * Context that is DRM GPUSVM is operating in (i.e. user arguments).
  */
···
 	unsigned int read_only :1;
 	unsigned int devmem_possible :1;
 	unsigned int devmem_only :1;
+	unsigned int allow_mixed :1;
 };
 
 int drm_gpusvm_init(struct drm_gpusvm *gpusvm,