Re: [PATCH i-g-t v7 1/9] drm-uapi/xe_drm: Sync with Add UAPI support for purgeable buffer objects

Kamil Konieczny
2026-04-09T15:42:47Z

Hi Arvind,
On 2026-04-09 at 12:31:10 +0530, Arvind Yadav wrote:
> From: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
>
> 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/GPU page faults return SIGBUS
>
> 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.
>
> Align with kernel 'commit f99a05cc0b85 ("drm/xe/uapi: Add UAPI support
> for purgeable buffer objects")'
>
> v2:
> - Update UAPI documentation to clarify retained must be initialized
> to 0(Thomas)
>
> v5:
> - Document DONTNEED BO access blocking behavior to prevent undefined
> behavior and clarify uAPI contract (Thomas, Matt)
> - Add query flag DRM_XE_QUERY_CONFIG_FLAG_HAS_PURGING_SUPPORT for
> feature detection. (Jose)
> - Renamed retained to retained_ptr. (Jose)
>
> v6:
> - Updated UAPI documentation as suggested. (Jose)
>
> v7:
> - Commit message updated with kernel UAPI details. (Nishit)
>
> Cc: Nishit Sharma <nishit.sharma@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Pravalika Gurram <pravalika.gurram@intel.com>
> Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>

Looks like this commit is already in igt so you could drop first
patch and resend. For example:

grep DRM_XE_VMA_ATTR_PURGEABLE_STATE include/drm-uapi/xe_drm.h

* - DRM_XE_VMA_ATTR_PURGEABLE_STATE: Set purgeable state for BOs.
#define DRM_XE_VMA_ATTR_PURGEABLE_STATE 3
* Used when @type == DRM_XE_VMA_ATTR_PURGEABLE_STATE.
/** @purge_state_val.val: value for DRM_XE_VMA_ATTR_PURGEABLE_STATE */

grep purge_state_val include/drm-uapi/xe_drm.h

* @purge_state_val: Purgeable state configuration
* Supported values for @purge_state_val.val:
/** @purge_state_val.val: value for DRM_XE_VMA_ATTR_PURGEABLE_STATE */
/** @purge_state_val.pad: MBZ */
* @purge_state_val.retained_ptr: Pointer to a __u32 output
} purge_state_val;

Regards,
Kamil

> ---
> include/drm-uapi/xe_drm.h | 69 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 69 insertions(+)
>
> diff --git a/include/drm-uapi/xe_drm.h b/include/drm-uapi/xe_drm.h
> index 077e66a68..cf0eb3f99 100644
> --- a/include/drm-uapi/xe_drm.h
> +++ b/include/drm-uapi/xe_drm.h
> @@ -431,6 +431,7 @@ struct drm_xe_query_config {
> #define DRM_XE_QUERY_CONFIG_FLAG_HAS_LOW_LATENCY (1 << 1)
> #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_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
> @@ -2067,6 +2068,7 @@ 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:
> *
> @@ -2099,6 +2101,7 @@ 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;
>
> @@ -2189,6 +2192,72 @@ 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 */
> --
> 2.43.0
>