drm/i915/gvt: Manage shadow pages with radix tree

We don't know how many page tables will be shadowed. It varies
considerably corresponding to guest load. Radix tree is a better
choice for us. Since Page Frame Number is used as key so most of
the bits are common.

Here is some performance data (duration in us) of looking up a
element:
Before: (aka. ppgtt_find_shadow_page)
 0.308 0.292 0.246 0.432 0.143 ... 0.311 0.225 0.382 0.199 0.325
After: (aka. intel_vgpu_find_spt_by_mfn)
 0.106 0.106 0.107 0.106 0.105 0.107 ... 0.107 0.109 0.105 0.108

This time I didn't get the early data of hash table. The data is
measured when desktop is shown.

As last change, the overall benchmark almost is not changed, but
we get better scalability.

Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/gtt.c

@@ -640,8 +640,8 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)
 
 	dma_unmap_page(kdev, spt->shadow_page.mfn << I915_GTT_PAGE_SHIFT, 4096,
 		       PCI_DMA_BIDIRECTIONAL);
-	if (!hlist_unhashed(&spt->node))
-		hash_del(&spt->node);
+
+	radix_tree_delete(&spt->vgpu->gtt.spt_tree, spt->shadow_page.mfn);
 
 	if (spt->guest_page.oos_page)
 		detach_oos_page(spt->vgpu, spt->guest_page.oos_page);
@@ -654,12 +654,14 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)
 
 static void ppgtt_free_all_spt(struct intel_vgpu *vgpu)
 {
-	struct hlist_node *n;
 	struct intel_vgpu_ppgtt_spt *spt;
-	int i;
+	struct radix_tree_iter iter;
+	void **slot;
 
-	hash_for_each_safe(vgpu->gtt.spt_hash_table, i, n, spt, node)
+	radix_tree_for_each_slot(slot, &vgpu->gtt.spt_tree, &iter, 0) {
+		spt = radix_tree_deref_slot(slot);
 		ppgtt_free_spt(spt);
+	}
 }
 
 static int ppgtt_handle_guest_write_page_table_bytes(
@@ -697,16 +699,10 @@ static struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_gfn(
 }
 
 /* Find the spt by shadow page mfn. */
-static struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_mfn(
+static inline struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_mfn(
 		struct intel_vgpu *vgpu, unsigned long mfn)
 {
-	struct intel_vgpu_ppgtt_spt *spt;
-
-	hash_for_each_possible(vgpu->gtt.spt_hash_table, spt, node, mfn) {
-		if (spt->shadow_page.mfn == mfn)
-			return spt;
-	}
-	return NULL;
+	return radix_tree_lookup(&vgpu->gtt.spt_tree, mfn);
 }
 
 static int reclaim_one_ppgtt_mm(struct intel_gvt *gvt);
@@ -741,8 +737,8 @@ retry:
 			     0, 4096, PCI_DMA_BIDIRECTIONAL);
 	if (dma_mapping_error(kdev, daddr)) {
 		gvt_vgpu_err("fail to map dma addr\n");
-		free_spt(spt);
-		return ERR_PTR(-EINVAL);
+		ret = -EINVAL;
+		goto err_free_spt;
 	}
 	spt->shadow_page.vaddr = page_address(spt->shadow_page.page);
 	spt->shadow_page.mfn = daddr >> I915_GTT_PAGE_SHIFT;
@@ -755,17 +751,23 @@ retry:
 
 	ret = intel_vgpu_register_page_track(vgpu, spt->guest_page.gfn,
 					ppgtt_write_protection_handler, spt);
-	if (ret) {
-		free_spt(spt);
-		dma_unmap_page(kdev, daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-		return ERR_PTR(ret);
-	}
+	if (ret)
+		goto err_unmap_dma;
 
-	INIT_HLIST_NODE(&spt->node);
-	hash_add(vgpu->gtt.spt_hash_table, &spt->node, spt->shadow_page.mfn);
+	ret = radix_tree_insert(&vgpu->gtt.spt_tree, spt->shadow_page.mfn, spt);
+	if (ret)
+		goto err_unreg_page_track;
 
 	trace_spt_alloc(vgpu->id, spt, type, spt->shadow_page.mfn, gfn);
 	return spt;
+
+err_unreg_page_track:
+	intel_vgpu_unregister_page_track(vgpu, spt->guest_page.gfn);
+err_unmap_dma:
+	dma_unmap_page(kdev, daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
+err_free_spt:
+	free_spt(spt);
+	return ERR_PTR(ret);
 }
 
 #define pt_entry_size_shift(spt) \
@@ -1994,7 +1996,7 @@ int intel_vgpu_init_gtt(struct intel_vgpu *vgpu)
 {
 	struct intel_vgpu_gtt *gtt = &vgpu->gtt;
 
-	hash_init(gtt->spt_hash_table);
+	INIT_RADIX_TREE(&gtt->spt_tree, GFP_KERNEL);
 
 	INIT_LIST_HEAD(&gtt->ppgtt_mm_list_head);
 	INIT_LIST_HEAD(&gtt->oos_page_list_head);
@@ -2024,7 +2026,7 @@ static void intel_vgpu_destroy_all_ppgtt_mm(struct intel_vgpu *vgpu)
 	if (GEM_WARN_ON(!list_empty(&vgpu->gtt.ppgtt_mm_list_head)))
 		gvt_err("vgpu ppgtt mm is not fully destoried\n");
 
-	if (GEM_WARN_ON(!hlist_empty(vgpu->gtt.spt_hash_table))) {
+	if (GEM_WARN_ON(!radix_tree_empty(&vgpu->gtt.spt_tree))) {
 		gvt_err("Why we still has spt not freed?\n");
 		ppgtt_free_all_spt(vgpu);
 	}