From: Himal Prasad Ghimiray Date: Thu, 26 Mar 2026 13:08:27 +0000 (+0530) Subject: drm/xe/uapi: Add UAPI support for purgeable buffer objects X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f99a05cc0b85fadd109fb3250fceccc5eaad3830;p=thirdparty%2Fkernel%2Flinux.git 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 Acked-by: José Roberto de Souza Reviewed-by: Thomas Hellström Signed-off-by: Himal Prasad Ghimiray Signed-off-by: Arvind Yadav Signed-off-by: Matthew Brost Link: https://patch.msgid.link/20260326130843.3545241-2-arvind.yadav@intel.com --- diff --git a/include/uapi/drm/xe_drm.h b/include/uapi/drm/xe_drm.h index 6c99514a85e14..ae2fda23ce7c7 100644 --- a/include/uapi/drm/xe_drm.h +++ b/include/uapi/drm/xe_drm.h @@ -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 */