drm/gpusvm: split MM state flags out of drm_gpusvm_pages_flags

drm_gpusvm_pages_flags currently mixes two status:
  - MM / virtual-address state: whether the range has been (partially)
    unmapped by the Linux MM, these follow the lifetime of the VMA and
    are a single per VA range fact.
  - Device mapping state: has_devmem_pages and has_dma_mapping,
    which describe the current page mapping status held by device
    itself.

Keeping both on the pages object blurs the semantics of the
abstraction of pages and VA range. So move the MM state flags onto the
range, and keep drm_gpusvm_pages_flags strictly for mapping state.

  - Introduce drm_gpusvm_range_flags { migrate_devmem, unmapped,
    partial_unmap } on drm_gpusvm_range.
  - Shrink drm_gpusvm_pages_flags to just has_devmem_pages and
    has_dma_mapping.

Side effect: drivers now need to check the unmap flags in the driver
itself to avoid handling the unmapped pages.

Mirror that bit onto drm_gpusvm_pages so the framework can
still short circuit drm_gpusvm_get_pages() under the notifier lock, and
make drm_gpusvm_range_set_unmapped() propagate it to the backing pages.
This follows Matt's review fixup for the v0 series; see the Link below.

Like drm_gpusvm_pages_flags, drm_gpusvm_range_flags unions its bits with
a u16 __flags member. Build the new value in a local copy and publish it
with a single WRITE_ONCE() on __flags, and have the lockless readers use
READ_ONCE(), so concurrent bitfield access stays data-race free and KCSAN
quiet.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://gitlab.freedesktop.org/mbrost/xe-kernel-driver-svn-perf-6-15-2025/-/commit/623f6a50c037d9e44f6c9fbe6859a0ba7ad50177
Signed-off-by: Honglei Huang <honghuan@amd.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260630102127.392396-2-honghuan@amd.com

1 files changed, 25 insertions, 5 deletions

diff --git a/include/drm/drm_gpusvm.h b/include/drm/drm_gpusvm.h
index 8a4d7134a9a7..251a7266a73f 100644
--- a/include/drm/drm_gpusvm.h
+++ b/include/drm/drm_gpusvm.h
@@ -109,9 +109,7 @@ struct drm_gpusvm_notifier {
 /**
  * struct drm_gpusvm_pages_flags - Structure representing a GPU SVM pages flags
  *
- * @migrate_devmem: Flag indicating whether the pages can be migrated to device memory
  * @unmapped: Flag indicating if the pages has been unmapped
- * @partial_unmap: Flag indicating if the pages has been partially unmapped
  * @has_devmem_pages: Flag indicating if the pages has devmem pages
  * @has_dma_mapping: Flag indicating if the pages has a DMA mapping
  * @__flags: Flags for pages in u16 form (used for READ_ONCE)
@@ -119,11 +117,8 @@ struct drm_gpusvm_notifier {
 struct drm_gpusvm_pages_flags {
 	union {
 		struct {
-			/* All flags below must be set upon creation */
-			u16 migrate_devmem : 1;
 			/* All flags below must be set / cleared under notifier lock */
 			u16 unmapped : 1;
-			u16 partial_unmap : 1;
 			u16 has_devmem_pages : 1;
 			u16 has_dma_mapping : 1;
 		};
@@ -152,6 +147,27 @@ struct drm_gpusvm_pages {
 };
 
 /**
+ * struct drm_gpusvm_range_flags - Range-level GPU SVM flags
+ *
+ * @migrate_devmem: Flag indicating whether the range can be migrated to device memory
+ * @unmapped: Flag indicating if the range has been unmapped
+ * @partial_unmap: Flag indicating if the range has been partially unmapped
+ * @__flags: All flags in u16 form (used for READ_ONCE)
+ */
+struct drm_gpusvm_range_flags {
+	union {
+		struct {
+			/* All flags below must be set upon creation */
+			u16 migrate_devmem	: 1;
+			/* All flags below must be set / cleared under notifier lock */
+			u16 unmapped		: 1;
+			u16 partial_unmap	: 1;
+		};
+		u16 __flags;
+	};
+};
+
+/**
  * struct drm_gpusvm_range - Structure representing a GPU SVM range
  *
  * @gpusvm: Pointer to the GPU SVM structure
@@ -160,6 +176,7 @@ struct drm_gpusvm_pages {
  * @itree: Interval tree node for the range (inserted in GPU SVM notifier)
  * @entry: List entry to fast interval tree traversal
  * @pages: The pages for this range.
+ * @flags: Flags for range see &struct drm_gpusvm_range_flags
  *
  * This structure represents a GPU SVM range used for tracking memory ranges
  * mapped in a DRM device.
@@ -171,6 +188,7 @@ struct drm_gpusvm_range {
 	struct interval_tree_node itree;
 	struct list_head entry;
 	struct drm_gpusvm_pages pages;
+	struct drm_gpusvm_range_flags flags;
 };
 
 /**
@@ -310,6 +328,8 @@ drm_gpusvm_range_find(struct drm_gpusvm_notifier *notifier, unsigned long start,
 		      unsigned long end);
 
 void drm_gpusvm_range_set_unmapped(struct drm_gpusvm_range *range,
+				   struct drm_gpusvm_pages *pages,
+				   unsigned int pages_count,
 				   const struct mmu_notifier_range *mmu_range);
 
 int drm_gpusvm_get_pages(struct drm_gpusvm *gpusvm,