[PATCH v8 5/6] drm/xe/pt: allow selecting the bind leaf PTE level

[Nareshkumar Gollakoti <naresh.kumar.g@intel.com>]

Add a target_leaf_level field to the page-table bind walk and use it to
    control the level at which leaf entries are emitted.

    By default, the bind walk emits level-0 leaf PTEs and relies on
    xe_pt_hugepte_possible() to select huge mappings when possible. Add an
    explicit target leaf level so the walk can stop earlier when the VMA
    requests a larger mapping size.

    Use level 1 for 2M PDE mappings and level 2 for 1G PDP mappings, while
    keeping level 0 for normal mappings. The existing huge-page heuristic
    is preserved for the default level-0 path.

    This allows the bind path to emit 2M and 1G leaf entries when requested
    by the VMA, while still validating alignment and size requirements.

    v2
    - avoid using max_level to control walk depth
    - use target_leaf_level to preserve the normal walk behavior
    - keep the default huge-page heuristic only for the level-0 path
    - refine commit message

    v3
    - reword commit message

    v4
    - allow fallback to smaller huge-page levels for non-zero
      target_leaf_level
    - avoid constraining clear_pt walks by target_leaf_level

    v5(Himal)
    - Restrict only intended level in debug page size policy mode
    - Allow the normal path to proceed smoothly when
      no debug page-size mode is selected.
    v8 (Himal)
    - Drop
      https://patchwork.freedesktop.org/patch/740059/?series=168905&rev=5
      patch and populate target_leaf_level from bo flags
    - populate target_leaf_level if it is in debug page size mode
      otherwise fill with 0 which is having no effect on the normal
      flow

Signed-off-by: Nareshkumar Gollakoti <naresh.kumar.g@intel.com>
---
 drivers/gpu/drm/xe/xe_pt.c | 77 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 75 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_pt.c b/drivers/gpu/drm/xe/xe_pt.c
index 598c6b2571e7..b360ef4e2a7e 100644
--- a/drivers/gpu/drm/xe/xe_pt.c
+++ b/drivers/gpu/drm/xe/xe_pt.c
@@ -302,6 +302,14 @@ struct xe_pt_stage_bind_walk {
 	bool needs_64K;
 	/** @clear_pt: clear page table entries during the bind walk */
 	bool clear_pt;
+	/**
+	 * @target_leaf_level: Page-table level at which to emit leaf PTEs
+	 * 0 for normal 4K/64K mappings, 1 for 2M huge pages, and 2 for 1G huge
+	 * pages. The walk still traverses from the root down; this field tells
+	 * xe_pt_stage_bind_entry() to treat the selected level as a leaf instead
+	 * of descending further.
+	 */
+	u32 target_leaf_level;
 	/**
 	 * @vma: VMA being mapped
 	 */
@@ -514,6 +522,39 @@ xe_pt_is_pte_ps64K(u64 addr, u64 next, struct xe_pt_stage_bind_walk *xe_walk)
 	return xe_walk->found_64K;
 }
 
+static bool xe_pt_huge_leaf_allowed(u64 addr, u64 next, unsigned int level,
+				    struct xe_pt_stage_bind_walk *xe_walk)
+{
+	if (xe_walk->clear_pt)
+		return xe_pt_hugepte_possible(addr, next, level, xe_walk);
+
+	if (!xe_debug_page_size_supported(xe_walk->vm->xe))
+		return xe_pt_hugepte_possible(addr, next, level, xe_walk);
+
+	if (!xe_walk->target_leaf_level)
+		return xe_pt_hugepte_possible(addr, next, level, xe_walk);
+
+	if (level == xe_walk->target_leaf_level)
+		return xe_pt_hugepte_possible(addr, next, level, xe_walk);
+
+	return false;
+}
+
+static bool xe_pt_exact_leaf_required_but_invalid(u64 addr, u64 next,
+						  unsigned int level,
+						  struct xe_pt_stage_bind_walk *xe_walk)
+{
+	struct xe_device *xe = xe_walk->vm->xe;
+
+	if (!xe_debug_page_size_mode_not_none(xe))
+		return false;
+
+	return !xe_walk->clear_pt &&
+		xe_walk->target_leaf_level &&
+		level == xe_walk->target_leaf_level &&
+		!xe_pt_hugepte_possible(addr, next, level, xe_walk);
+}
+
 static int
 xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset,
 		       unsigned int level, u64 addr, u64 next,
@@ -531,8 +572,18 @@ xe_pt_stage_bind_entry(struct xe_ptw *parent, pgoff_t offset,
 	int ret = 0;
 	u64 pte;
 
-	/* Is this a leaf entry ?*/
-	if (level == 0 || xe_pt_hugepte_possible(addr, next, level, xe_walk)) {
+	if (xe_pt_exact_leaf_required_but_invalid(addr, next, level, xe_walk))
+		return -EINVAL;
+
+	/*
+	 * Is this a leaf entry?
+	 * Always create a 4K leaf at level 0. For huge pages (level > 0),
+	 * validate alignment and size with xe_pt_hugepte_possible().
+	 * When target_leaf_level is non-zero, only that huge-page level is
+	 * accepted for normal bind walks. Clear walks remain unconstrained so
+	 * existing huge leaves can be cleared without descending further.
+	 */
+	if (level == 0 || xe_pt_huge_leaf_allowed(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_or_purged = xe_vma_is_null(xe_walk->vma) ||
@@ -682,6 +733,27 @@ static bool xe_atomic_for_system(struct xe_vm *vm, struct xe_vma *vma)
 				 (bo && xe_bo_has_single_placement(bo))));
 }
 
+static u32 xe_pt_target_leaf_level_from_bo(struct xe_device *xe,
+					   struct xe_vma *vma)
+{
+	struct xe_bo *bo = xe_vma_bo(vma);
+
+	if (!xe_debug_page_size_mode_not_none(xe))
+		return 0;
+
+	if (!bo || !(bo->flags & XE_BO_FLAG_VRAM_MASK) ||
+	    !(bo->flags & XE_BO_FLAG_USER))
+		return 0;
+
+	if (bo->flags & XE_BO_FLAG_NEEDS_1G)
+		return 2;
+
+	if (bo->flags & XE_BO_FLAG_NEEDS_2M)
+		return 1;
+
+	return 0;
+}
+
 /**
  * xe_pt_stage_bind() - Build a disconnected page-table tree for a given address
  * range.
@@ -774,6 +846,7 @@ xe_pt_stage_bind(struct xe_tile *tile, struct xe_vma *vma,
 		xe_svm_notifier_unlock(vm);
 	}
 
+	xe_walk.target_leaf_level = xe_pt_target_leaf_level_from_bo(xe, vma);
 	xe_walk.needs_64K = (vm->flags & XE_VM_FLAG_64K);
 	if (clear_pt)
 		goto walk_pt;
-- 
2.43.0