[RFC PATCH 02/12] KVM: arm64: Allow visiting block PTEs in post-order

[Ricardo Koller <ricarkol@google.com>]

The page table walker does not visit block PTEs in post-order. But there
are some cases where doing so would be beneficial, for example: breaking a
1G block PTE into a full tree in post-order avoids visiting the new tree.

Allow post order visits of block PTEs. This will be used in a subsequent
commit for eagerly breaking huge pages.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
---
 arch/arm64/include/asm/kvm_pgtable.h |  4 ++--
 arch/arm64/kvm/hyp/nvhe/setup.c      |  2 +-
 arch/arm64/kvm/hyp/pgtable.c         | 25 ++++++++++++-------------
 3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index e2edeed462e8..d2e4a5032146 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -255,7 +255,7 @@ struct kvm_pgtable {
  *					entries.
  * @KVM_PGTABLE_WALK_TABLE_PRE:		Visit table entries before their
  *					children.
- * @KVM_PGTABLE_WALK_TABLE_POST:	Visit table entries after their
+ * @KVM_PGTABLE_WALK_POST:		Visit leaf or table entries after their
  *					children.
  * @KVM_PGTABLE_WALK_SHARED:		Indicates the page-tables may be shared
  *					with other software walkers.
@@ -263,7 +263,7 @@ struct kvm_pgtable {
 enum kvm_pgtable_walk_flags {
 	KVM_PGTABLE_WALK_LEAF			= BIT(0),
 	KVM_PGTABLE_WALK_TABLE_PRE		= BIT(1),
-	KVM_PGTABLE_WALK_TABLE_POST		= BIT(2),
+	KVM_PGTABLE_WALK_POST			= BIT(2),
 	KVM_PGTABLE_WALK_SHARED			= BIT(3),
 };
 
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index b47d969ae4d3..b0c1618d053b 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -265,7 +265,7 @@ static int fix_hyp_pgtable_refcnt(void)
 {
 	struct kvm_pgtable_walker walker = {
 		.cb	= fix_hyp_pgtable_refcnt_walker,
-		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
+		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_POST,
 		.arg	= pkvm_pgtable.mm_ops,
 	};
 
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b16107bf917c..1b371f6dbac2 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -206,16 +206,15 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 	if (!table) {
 		data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level));
 		data->addr += kvm_granule_size(level);
-		goto out;
+	} else {
+		childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
+		ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
+		if (ret)
+			goto out;
 	}
 
-	childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
-	ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
-	if (ret)
-		goto out;
-
-	if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST)
-		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST);
+	if (ctx.flags & KVM_PGTABLE_WALK_POST)
+		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_POST);
 
 out:
 	return ret;
@@ -494,7 +493,7 @@ u64 kvm_pgtable_hyp_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
 	struct kvm_pgtable_walker walker = {
 		.cb	= hyp_unmap_walker,
 		.arg	= &unmapped,
-		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
+		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_POST,
 	};
 
 	if (!pgt->mm_ops->page_count)
@@ -542,7 +541,7 @@ void kvm_pgtable_hyp_destroy(struct kvm_pgtable *pgt)
 {
 	struct kvm_pgtable_walker walker = {
 		.cb	= hyp_free_walker,
-		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
+		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_POST,
 	};
 
 	WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
@@ -1003,7 +1002,7 @@ int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size)
 	struct kvm_pgtable_walker walker = {
 		.cb	= stage2_unmap_walker,
 		.arg	= pgt,
-		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST,
+		.flags	= KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_POST,
 	};
 
 	return kvm_pgtable_walk(pgt, addr, size, &walker);
@@ -1234,7 +1233,7 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
 	struct kvm_pgtable_walker walker = {
 		.cb	= stage2_free_walker,
 		.flags	= KVM_PGTABLE_WALK_LEAF |
-			  KVM_PGTABLE_WALK_TABLE_POST,
+			  KVM_PGTABLE_WALK_POST,
 	};
 
 	WARN_ON(kvm_pgtable_walk(pgt, 0, BIT(pgt->ia_bits), &walker));
@@ -1249,7 +1248,7 @@ void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pg
 	struct kvm_pgtable_walker walker = {
 		.cb	= stage2_free_walker,
 		.flags	= KVM_PGTABLE_WALK_LEAF |
-			  KVM_PGTABLE_WALK_TABLE_POST,
+			  KVM_PGTABLE_WALK_POST,
 	};
 	struct kvm_pgtable_walk_data data = {
 		.walker	= &walker,
-- 
2.38.1.431.g37b22c650d-goog