[PATCH v4] drm/gpusvm, drm/xe: Allow mixed mappings for userptr

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

From: Matthew Brost <matthew.brost@intel.com>

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 <maarten.lankhorst@intel.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
---
 drivers/gpu/drm/drm_gpusvm.c    | 6 ++++--
 drivers/gpu/drm/xe/xe_userptr.c | 4 +++-
 include/drm/drm_gpusvm.h        | 4 ++++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gpusvm.c b/drivers/gpu/drm/drm_gpusvm.c
index cb906765897e..73e550c8ff8c 100644
--- a/drivers/gpu/drm/drm_gpusvm.c
+++ b/drivers/gpu/drm/drm_gpusvm.c
@@ -1363,7 +1363,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 		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;
 			}
@@ -1399,7 +1400,8 @@ int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,
 		} 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;
 			}
diff --git a/drivers/gpu/drm/xe/xe_userptr.c b/drivers/gpu/drm/xe/xe_userptr.c
index f16e92cd8090..0d9130b1958a 100644
--- a/drivers/gpu/drm/xe/xe_userptr.c
+++ b/drivers/gpu/drm/xe/xe_userptr.c
@@ -3,6 +3,7 @@
  * Copyright © 2025 Intel Corporation
  */
 
+#include "xe_svm.h"
 #include "xe_userptr.h"
 
 #include <linux/mm.h>
@@ -54,7 +55,8 @@ int xe_vma_userptr_pin_pages(struct xe_userptr_vma *uvma)
 	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);
diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
index b92faa9a26b2..632e100e6efb 100644
--- a/include/drm/drm_gpusvm.h
+++ b/include/drm/drm_gpusvm.h
@@ -235,6 +235,9 @@ struct drm_gpusvm {
  * @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).
  */
@@ -246,6 +249,7 @@ struct drm_gpusvm_ctx {
 	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,
-- 
2.51.0