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

Yadav, Arvind
2026-04-10T05:36:17Z

On 09-04-2026 21:12, Kamil Konieczny wrote:
> 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;

Noted, I will drop this patch.

Thanks,
Arvind

>
> 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
>>