Commit f99a05cc authored by Himal Prasad Ghimiray's avatar Himal Prasad Ghimiray Committed by Matthew Brost
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drm/xe/uapi: Add UAPI support for purgeable buffer objects 



Extend the DRM_XE_MADVISE ioctl to support purgeable buffer object
management by adding DRM_XE_VMA_ATTR_PURGEABLE_STATE attribute type.

This allows userspace applications to provide memory usage hints to
the kernel for better memory management under pressure:

- WILLNEED: Buffer is needed and should not be purged. If the BO was
  previously purged, retained field returns 0 indicating backing store
  was lost (once purged, always purged semantics matching i915).

- DONTNEED: Buffer is not currently needed and may be purged by the
  kernel under memory pressure to free resources. Only applies to
  non-shared BOs.

  To prevent undefined behavior, the following operations are blocked
  while a BO is in DONTNEED state:
  - New mmap() operations return -EBUSY
  - VM_BIND operations return -EBUSY
  - New dma-buf exports return -EBUSY
  - CPU page faults return SIGBUS
  - GPU page faults fail with -EACCES

  This ensures applications cannot use a BO while marked as DONTNEED,
  preventing erratic behavior when the kernel purges the backing store.

The implementation includes a 'retained' output field (matching i915's
drm_i915_gem_madvise.retained) that indicates whether the BO's backing
store still exists (1) or has been purged (0).

Added DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING_SUPPORT flag to allow
userspace to detect kernel support for purgeable buffer objects
before attempting to use the feature.

Cc: Matthew Brost <matthew.brost@intel.com>
Acked-by: default avatarJosé Roberto de Souza <jose.souza@intel.com>
Reviewed-by: default avatarThomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: default avatarHimal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: default avatarArvind Yadav <arvind.yadav@intel.com>
Signed-off-by: default avatarMatthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260326130843.3545241-2-arvind.yadav@intel.com
parent b6df77f4

include/uapi/drm/xe_drm.h

+69 −0
Original line number Diff line number Diff line
@@ -432,6 +432,7 @@ struct drm_xe_query_config { 
	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_CPU_ADDR_MIRROR	(1 << 2)

	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_NO_COMPRESSION_HINT (1 << 3)

	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_DISABLE_STATE_CACHE_PERF_FIX	(1 << 4)

	#define DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING_SUPPORT    (1 << 5)

#define DRM_XE_QUERY_CONFIG_MIN_ALIGNMENT		2

#define DRM_XE_QUERY_CONFIG_VA_BITS			3

#define DRM_XE_QUERY_CONFIG_MAX_EXEC_QUEUE_PRIORITY	4
@@ -2171,6 +2172,7 @@ struct drm_xe_query_eu_stall { 
 *  - DRM_XE_MEM_RANGE_ATTR_PREFERRED_LOC: Set preferred memory location.

 *  - DRM_XE_MEM_RANGE_ATTR_ATOMIC: Set atomic access policy.

 *  - DRM_XE_MEM_RANGE_ATTR_PAT: Set page attribute table index.

 *  - DRM_XE_VMA_ATTR_PURGEABLE_STATE: Set purgeable state for BOs.

 *

 * Example:

 *
@@ -2203,6 +2205,7 @@ struct drm_xe_madvise { 
#define DRM_XE_MEM_RANGE_ATTR_PREFERRED_LOC	0

#define DRM_XE_MEM_RANGE_ATTR_ATOMIC		1

#define DRM_XE_MEM_RANGE_ATTR_PAT		2

#define DRM_XE_VMA_ATTR_PURGEABLE_STATE		3

	/** @type: type of attribute */

	__u32 type;
@@ -2293,6 +2296,72 @@ struct drm_xe_madvise { 
			/** @pat_index.reserved: Reserved */

			__u64 reserved;

		} pat_index;



		/**

		 * @purge_state_val: Purgeable state configuration

		 *

		 * Used when @type == DRM_XE_VMA_ATTR_PURGEABLE_STATE.

		 *

		 * Configures the purgeable state of buffer objects in the specified

		 * virtual address range. This allows applications to hint to the kernel

		 * about bo's usage patterns for better memory management.

		 *

		 * By default all VMAs are in WILLNEED state.

		 *

		 * Supported values for @purge_state_val.val:

		 *  - DRM_XE_VMA_PURGEABLE_STATE_WILLNEED (0): Marks BO as needed.

		 *    If the BO was previously purged, the kernel sets the __u32 at

		 *    @retained_ptr to 0 (backing store lost) so the application knows

		 *    it must recreate the BO.

		 *

		 *  - DRM_XE_VMA_PURGEABLE_STATE_DONTNEED (1): Marks BO as not currently

		 *    needed. Kernel may purge it under memory pressure to reclaim memory.

		 *    Only applies to non-shared BOs. The kernel sets the __u32 at

		 *    @retained_ptr to 1 if the backing store still exists (not yet purged),

		 *    or 0 if it was already purged.

		 *

		 *    Important: Once marked as DONTNEED, touching the BO's memory

		 *    is undefined behavior. It may succeed temporarily (before the

		 *    kernel purges the backing store) but will suddenly fail once

		 *    the BO transitions to PURGED state.

		 *

		 *    To transition back: use WILLNEED and check @retained_ptr —

		 *    if 0, backing store was lost and the BO must be recreated.

		 *

		 *    The following operations are blocked in DONTNEED state to

		 *    prevent the BO from being re-mapped after madvise:

		 *    - New mmap() calls: Fail with -EBUSY

		 *    - VM_BIND operations: Fail with -EBUSY

		 *    - New dma-buf exports: Fail with -EBUSY

		 *    - CPU page faults (existing mmap): Fail with SIGBUS

		 *    - GPU page faults (fault-mode VMs): Fail with -EACCES

		 */

		struct {

#define DRM_XE_VMA_PURGEABLE_STATE_WILLNEED	0

#define DRM_XE_VMA_PURGEABLE_STATE_DONTNEED	1

			/** @purge_state_val.val: value for DRM_XE_VMA_ATTR_PURGEABLE_STATE */

			__u32 val;



			/** @purge_state_val.pad: MBZ */

			__u32 pad;

			/**

			 * @purge_state_val.retained_ptr: Pointer to a __u32 output

			 * field for backing store status.

			 *

			 * Userspace must initialize the __u32 value at this address

			 * to 0 before the ioctl. Kernel writes a __u32 after the

			 * operation:

			 * - 1 if backing store exists (not purged)

			 * - 0 if backing store was purged

			 *

			 * If userspace fails to initialize to 0, ioctl returns -EINVAL.

			 * This ensures a safe default (0 = assume purged) if kernel

			 * cannot write the result.

			 *

			 * Similar to i915's drm_i915_gem_madvise.retained field.

			 */

			__u64 retained_ptr;

		} purge_state_val;

	};



	/** @reserved: Reserved */