drm/xe/uapi: Extend the madvise functionality to support foreign pagemap placement for svm

Use device file descriptors and regions to represent pagemaps on
foreign or local devices.

The underlying files are type-checked at madvise time, and
references are kept on the drm_pagemap as long as there is are
madvises pointing to it.

Extend the madvise preferred_location UAPI to support the region
instance to identify the foreign placement.

v2:
- Improve UAPI documentation. (Matt Brost)
- Sanitize preferred_mem_loc.region_instance madvise. (Matt Brost)
- Clarify madvise drm_pagemap vs xe_pagemap refcounting. (Matt Brost)
- Don't allow a foreign drm_pagemap madvise without a fast
  interconnect.
v3:
- Add a comment about reference-counting in xe_devmem_open() and
  remove the reference-count get-and-put. (Matt Brost)

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20251219113320.183860-16-thomas.hellstrom@linux.intel.com

1 files changed, 15 insertions, 3 deletions

diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h
index 726e481574fe..bb69f9b30c7d 100644
--- a/include/uapi/drm/xe_drm.h
+++ b/include/uapi/drm/xe_drm.h
@@ -2123,7 +2123,13 @@ struct drm_xe_madvise {
 		struct {
 #define DRM_XE_PREFERRED_LOC_DEFAULT_DEVICE	0
 #define DRM_XE_PREFERRED_LOC_DEFAULT_SYSTEM	-1
-			/** @preferred_mem_loc.devmem_fd: fd for preferred loc */
+			/**
+			 * @preferred_mem_loc.devmem_fd:
+			 * Device file-descriptor of the device where the
+			 * preferred memory is located, or one of the
+			 * above special values. Please also see
+			 * @preferred_mem_loc.region_instance below.
+			 */
 			__u32 devmem_fd;
 
 #define DRM_XE_MIGRATE_ALL_PAGES		0
@@ -2131,8 +2137,14 @@ struct drm_xe_madvise {
 			/** @preferred_mem_loc.migration_policy: Page migration policy */
 			__u16 migration_policy;
 
-			/** @preferred_mem_loc.pad : MBZ */
-			__u16 pad;
+			/**
+			 * @preferred_mem_loc.region_instance : Region instance.
+			 * MBZ if @devmem_fd <= &DRM_XE_PREFERRED_LOC_DEFAULT_DEVICE.
+			 * Otherwise should point to the desired device
+			 * VRAM instance of the device indicated by
+			 * @preferred_mem_loc.devmem_fd.
+			 */
+			__u16 region_instance;
 
 			/** @preferred_mem_loc.reserved : Reserved */
 			__u64 reserved;