On Mon, Dec 01, 2025 at 11:20:14AM +0530, Arvind Yadav wrote:This allows userspace applications to provide memory usage hints to the kernel for better memory management under pressure: Add the core implementation for purgeable buffer objects, enabling memory reclamation of user-designated DONTNEED buffers during eviction. This patch implements the purge operation and state machine transitions: Purgeable States (from xe_madv_purgeable_state): - WILLNEED (0): BO should be retained, actively used - DONTNEED (1): BO eligible for purging, not currently neededQuick comment - should we use TTM priority levels so WILLNEED is a higher priority (less likely to be evicted) than DONTNEED (more likely to be evicted). Expect more comments but just a quick thought.
Yes, we should leverage TTM priority levels for better eviction
ordering.
Currently TTM has separate LRU lists per priority
(man->lru[TTM_MAX_BO_PRIORITY]),
and eviction walks the lists starting from lower priority BOs
first.
1. Set DONTNEED BOs to priority 0 (evicted first, before normal
BOs)
2. Keep WILLNEED BOs at priority ' XE_BO_PRIORITY_NORMAL' (normal
eviction order)
~Arvind
Matt- PURGED (2): BO backing store reclaimed, permanently invalid Design Rationale: - Async TLB invalidation via trigger_rebind (no blocking xe_vm_invalidate_vma) - i915 compatibility: retained field, "once purged always purged" semantics - Shared BO protection prevents multi-process memory corruption - Scratch PTE reuse avoids new infrastructure, safe for fault mode v2: - Use xe_bo_trigger_rebind() for async TLB invalidation (Thomas Hellström) - Add NULL rebind with scratch PTEs for fault mode (Thomas Hellström) - Implement i915-compatible retained field logic (Thomas Hellström) - Skip BO validation for purged BOs in page fault handler (crash fix) - Add scratch VM check in page fault path (non-scratch VMs fail fault) - Force clear_pt for non-scratch VMs to avoid phys addr 0 mapping (review fix) - Add !is_purged check to resource cursor setup to prevent stale access Cc: Matthew Brost <matthew.brost@intel.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com> --- drivers/gpu/drm/xe/xe_bo.c | 72 ++++++++++++++++++++++----- drivers/gpu/drm/xe/xe_gt_pagefault.c | 19 ++++++++ drivers/gpu/drm/xe/xe_pt.c | 36 ++++++++++++-- drivers/gpu/drm/xe/xe_vm.c | 11 ++++- drivers/gpu/drm/xe/xe_vm_madvise.c | 73 ++++++++++++++++++++++++++++ 5 files changed, 193 insertions(+), 18 deletions(-) diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c index cbc3ee157218..f0b3f7a13114 100644 --- a/drivers/gpu/drm/xe/xe_bo.c +++ b/drivers/gpu/drm/xe/xe_bo.c @@ -836,6 +836,53 @@ static int xe_bo_move_notify(struct xe_bo *bo, return 0; } +static void xe_bo_set_purged(struct xe_bo *bo) +{ + /* BO must be locked before modifying madv state */ + dma_resv_assert_held(bo->ttm.base.resv); + + atomic_set(&bo->madv_purgeable, XE_MADV_PURGEABLE_PURGED); +} + +/** + * xe_ttm_bo_purge() - Purge buffer object backing store + * @ttm_bo: The TTM buffer object to purge + * @ctx: TTM operation context + * + * This function purges the backing store of a BO marked as DONTNEED and + * triggers rebind to invalidate stale GPU mappings. For fault-mode VMs, + * this zaps the PTEs. The next GPU access will trigger a page fault and + * perform NULL rebind (scratch pages or clear PTEs based on VM config). + */ +static void xe_ttm_bo_purge(struct ttm_buffer_object *ttm_bo, struct ttm_operation_ctx *ctx) +{ + struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev); + struct xe_bo *bo = ttm_to_xe_bo(ttm_bo); + + if (ttm_bo->ttm) { + struct ttm_placement place = {}; + int ret = ttm_bo_validate(ttm_bo, &place, ctx); + + drm_WARN_ON(&xe->drm, ret); + if (!ret && bo) { + if (atomic_read(&bo->madv_purgeable) == XE_MADV_PURGEABLE_DONTNEED) { + xe_bo_set_purged(bo); + + /* + * Trigger rebind to invalidate stale GPU mappings. + * - Non-fault mode: Marks VMAs for rebind + * - Fault mode: Zaps PTEs (sets to 0), next access triggers fault + * and NULL rebind with scratch/clear PTEs per VM config + */ + ret = xe_bo_trigger_rebind(xe, bo, ctx); + if (ret) + drm_warn(&xe->drm, + "Failed to invalidate purged BO: %d\n", ret); + } + } + } +} + static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict, struct ttm_operation_ctx *ctx, struct ttm_resource *new_mem, @@ -853,8 +900,18 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict, bool needs_clear; bool handle_system_ccs = (!IS_DGFX(xe) && xe_bo_needs_ccs_pages(bo) && ttm && ttm_tt_is_populated(ttm)) ? true : false; + int state = atomic_read(&bo->madv_purgeable); int ret = 0; + /* + * Purge only non-shared BOs explicitly marked DONTNEED by userspace. + * The move_notify callback will handle invalidation asynchronously. + */ + if (evict && state == XE_MADV_PURGEABLE_DONTNEED && !xe_bo_is_shared_locked(bo)) { + xe_ttm_bo_purge(ttm_bo, ctx); + return 0; + } + /* Bo creation path, moving to system or TT. */ if ((!old_mem && ttm) && !handle_system_ccs) { if (new_mem->mem_type == XE_PL_TT) @@ -1606,18 +1663,6 @@ static void xe_ttm_bo_delete_mem_notify(struct ttm_buffer_object *ttm_bo) } } -static void xe_ttm_bo_purge(struct ttm_buffer_object *ttm_bo, struct ttm_operation_ctx *ctx) -{ - struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev); - - if (ttm_bo->ttm) { - struct ttm_placement place = {}; - int ret = ttm_bo_validate(ttm_bo, &place, ctx); - - drm_WARN_ON(&xe->drm, ret); - } -} - static void xe_ttm_bo_swap_notify(struct ttm_buffer_object *ttm_bo) { struct ttm_operation_ctx ctx = { @@ -2202,6 +2247,9 @@ struct xe_bo *xe_bo_init_locked(struct xe_device *xe, struct xe_bo *bo, #endif INIT_LIST_HEAD(&bo->vram_userfault_link); + /* Initialize purge advisory state */ + atomic_set(&bo->madv_purgeable, XE_MADV_PURGEABLE_WILLNEED); + drm_gem_private_object_init(&xe->drm, &bo->ttm.base, size); if (resv) { diff --git a/drivers/gpu/drm/xe/xe_gt_pagefault.c b/drivers/gpu/drm/xe/xe_gt_pagefault.c index a054d6010ae0..8c7e5dcb627b 100644 --- a/drivers/gpu/drm/xe/xe_gt_pagefault.c +++ b/drivers/gpu/drm/xe/xe_gt_pagefault.c @@ -87,6 +87,13 @@ static int xe_pf_begin(struct drm_exec *exec, struct xe_vma *vma, if (!bo) return 0; + /* + * Skip validation/migration for purged BOs - they have no backing pages. + * Rebind will use scratch PTEs instead. + */ + if (xe_bo_is_purged(bo)) + return 0; + return need_vram_move ? xe_bo_migrate(bo, vram->placement, NULL, exec) : xe_bo_validate(bo, vm, true, exec); } @@ -100,9 +107,21 @@ static int handle_vma_pagefault(struct xe_gt *gt, struct xe_vma *vma, struct drm_exec exec; struct dma_fence *fence; int err, needs_vram; + struct xe_bo *bo; lockdep_assert_held_write(&vm->lock); + /* + * Check if BO is purged. For purged BOs: + * - Scratch VMs: Allow rebind with scratch PTEs (safe zero reads) + * - Non-scratch VMs: FAIL the page fault (no scratch page available) + */ + bo = xe_vma_bo(vma); + if (bo && xe_bo_is_purged(bo)) { + if (!xe_vm_has_scratch(vm)) + return -EACCES; + } + needs_vram = xe_vma_need_vram_for_atomic(vm->xe, vma, atomic); if (needs_vram < 0 || (needs_vram && xe_vma_is_userptr(vma))) return needs_vram < 0 ? needs_vram : -EACCES; diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c index d22fd1ccc0ba..062f64b16a58 100644 --- a/drivers/gpu/drm/xe/xe_pt.c +++ b/drivers/gpu/drm/xe/xe_pt.c @@ -533,20 +533,26 @@ xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset, /* Is this a leaf entry ?*/ if (level == 0 || xe_pt_hugepte_possible(addr, next, level, xe_walk)) { struct xe_res_cursor *curs = xe_walk->curs; + struct xe_bo *bo = xe_vma_bo(xe_walk->vma); bool is_null = xe_vma_is_null(xe_walk->vma); - bool is_vram = is_null ? false : xe_res_is_vram(curs); + bool is_purged = bo && xe_bo_is_purged(bo); + bool is_vram = (is_null || is_purged) ? false : xe_res_is_vram(curs); XE_WARN_ON(xe_walk->va_curs_start != addr); if (xe_walk->clear_pt) { pte = 0; } else { - pte = vm->pt_ops->pte_encode_vma(is_null ? 0 : + /* + * For purged BOs, treat like null VMAs - pass address 0. + * The pte_encode_vma will set XE_PTE_NULL flag for scratch mapping. + */ + pte = vm->pt_ops->pte_encode_vma((is_null || is_purged) ? 0 : xe_res_dma(curs) + xe_walk->dma_offset, xe_walk->vma, pat_index, level); - if (!is_null) + if (!is_null && !is_purged) pte |= is_vram ? xe_walk->default_vram_pte : xe_walk->default_system_pte; @@ -570,7 +576,7 @@ xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset, if (unlikely(ret)) return ret; - if (!is_null && !xe_walk->clear_pt) + if (!is_null && !is_purged && !xe_walk->clear_pt) xe_res_next(curs, next - addr); xe_walk->va_curs_start = next; xe_walk->vma->gpuva.flags |= (XE_VMA_PTE_4K << level); @@ -723,6 +729,26 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma, }; struct xe_pt *pt = vm->pt_root[tile->id]; int ret; + bool is_purged = false; + + /* + * Check if BO is purged: + * - Scratch VMs: Use scratch PTEs (XE_PTE_NULL) for safe zero reads + * - Non-scratch VMs: Clear PTEs to zero (non-present) to avoid mapping to phys addr 0 + * + * For non-scratch VMs, we force clear_pt=true so leaf PTEs become completely + * zero instead of creating a PRESENT mapping to physical address 0. + */ + if (bo && xe_bo_is_purged(bo)) { + is_purged = true; + + /* + * For non-scratch VMs, a NULL rebind should use zero PTEs + * (non-present), not a present PTE to phys 0. + */ + if (!xe_vm_has_scratch(vm)) + xe_walk.clear_pt = true; + } if (range) { /* Move this entire thing to xe_svm.c? */ @@ -762,7 +788,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma, if (!range) xe_bo_assert_held(bo); - if (!xe_vma_is_null(vma) && !range) { + if (!xe_vma_is_null(vma) && !range && !is_purged) { if (xe_vma_is_userptr(vma)) xe_res_first_dma(to_userptr_vma(vma)->userptr.pages.dma_addr, 0, xe_vma_size(vma), &curs); diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c index 10d77666a425..d03e69524369 100644 --- a/drivers/gpu/drm/xe/xe_vm.c +++ b/drivers/gpu/drm/xe/xe_vm.c @@ -1336,6 +1336,9 @@ static u64 xelp_pte_encode_bo(struct xe_bo *bo, u64 bo_offset, static u64 xelp_pte_encode_vma(u64 pte, struct xe_vma *vma, u16 pat_index, u32 pt_level) { + struct xe_bo *bo = xe_vma_bo(vma); + struct xe_vm *vm = xe_vma_vm(vma); + pte |= XE_PAGE_PRESENT; if (likely(!xe_vma_read_only(vma))) @@ -1344,7 +1347,13 @@ static u64 xelp_pte_encode_vma(u64 pte, struct xe_vma *vma, pte |= pte_encode_pat_index(pat_index, pt_level); pte |= pte_encode_ps(pt_level); - if (unlikely(xe_vma_is_null(vma))) + /* + * NULL PTEs redirect to scratch page (return zeros on read). + * Set for: 1) explicit null VMAs, 2) purged BOs on scratch VMs. + * Never set NULL flag without scratch page - causes undefined behavior. + */ + if (unlikely(xe_vma_is_null(vma) || + (bo && xe_bo_is_purged(bo) && xe_vm_has_scratch(vm)))) pte |= XE_PTE_NULL; return pte; diff --git a/drivers/gpu/drm/xe/xe_vm_madvise.c b/drivers/gpu/drm/xe/xe_vm_madvise.c index cad3cf627c3f..3ba851e0b870 100644 --- a/drivers/gpu/drm/xe/xe_vm_madvise.c +++ b/drivers/gpu/drm/xe/xe_vm_madvise.c @@ -158,6 +158,60 @@ static void madvise_pat_index(struct xe_device *xe, struct xe_vm *vm, } } +/* + * Handle purgeable buffer object advice for DONTNEED/WILLNEED/PURGED. + * Updates op->purge_state_val.retained to indicate if backing store + * exists (matches i915's retained). + */ +static void xe_vm_madvise_purgeable_bo(struct xe_device *xe, struct xe_vm *vm, + struct xe_vma **vmas, int num_vmas, + struct drm_xe_madvise *op) +{ + bool has_purged_bo = false; + int i; + + xe_assert(vm->xe, op->type == DRM_XE_VMA_ATTR_PURGEABLE_STATE); + + for (i = 0; i < num_vmas; i++) { + struct xe_bo *bo = xe_vma_bo(vmas[i]); + + if (!bo) + continue; + + /* BO must be locked before modifying madv state */ + dma_resv_assert_held(bo->ttm.base.resv); + + /* + * Once purged, always purged. Cannot transition back to WILLNEED. + * This matches i915 semantics where purged BOs are permanently invalid. + */ + if (xe_bo_is_purged(bo)) { + has_purged_bo = true; + continue; + } + + switch (op->purge_state_val.val) { + case DRM_XE_VMA_PURGEABLE_STATE_WILLNEED: + atomic_set(&bo->madv_purgeable, XE_MADV_PURGEABLE_WILLNEED); + break; + case DRM_XE_VMA_PURGEABLE_STATE_DONTNEED: + if (!xe_bo_is_shared_locked(bo)) + atomic_set(&bo->madv_purgeable, XE_MADV_PURGEABLE_DONTNEED); + break; + default: + drm_warn(&vm->xe->drm, "Invalid madvice value = %d\n", + op->purge_state_val.val); + return; + } + } + + /* + * Set retained flag to indicate if backing store still exists. + * Matches i915: retained = 1 if not purged, 0 if purged. + */ + op->purge_state_val.retained = !has_purged_bo; +} + typedef void (*madvise_func)(struct xe_device *xe, struct xe_vm *vm, struct xe_vma **vmas, int num_vmas, struct drm_xe_madvise *op); @@ -283,6 +337,19 @@ static bool madvise_args_are_sane(struct xe_device *xe, const struct drm_xe_madv return false; break; } + case DRM_XE_VMA_ATTR_PURGEABLE_STATE: + { + u32 val = args->purge_state_val.val; + + if (XE_IOCTL_DBG(xe, !((val == DRM_XE_VMA_PURGEABLE_STATE_WILLNEED) || + (val == DRM_XE_VMA_PURGEABLE_STATE_DONTNEED)))) + return false; + + if (XE_IOCTL_DBG(xe, args->purge_state_val.reserved)) + return false; + + break; + } default: if (XE_IOCTL_DBG(xe, 1)) return false; @@ -402,6 +469,12 @@ int xe_vm_madvise_ioctl(struct drm_device *dev, void *data, struct drm_file *fil goto err_fini; } } + if (args->type == DRM_XE_VMA_ATTR_PURGEABLE_STATE) { + xe_vm_madvise_purgeable_bo(xe, vm, madvise_range.vmas, + madvise_range.num_vmas, args); + goto err_fini; + + } } if (madvise_range.has_svm_userptr_vmas) { -- 2.43.0