[RFC PATCH 1/2] KVM: arm64: Introduce S2 walker SKIP return options

[Leonardo Bras <leo.bras@arm.com>]

Introduce S2 walker return values:
- SKIP_CHILDREN: skip walking the children of the current node
- SKIP_SIBLINGS: skip waling the siblings of the current node

Also, modify __kvm_pgtable_visit() to fulfil the hing on above return
values. Current walkers should not be impacted

Signed-off-by: Leonardo Bras <leo.bras@arm.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 0c1defa5fb0f..4e43339522bb 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -12,20 +12,26 @@
 #include <asm/stage2_pgtable.h>
 
 struct kvm_pgtable_walk_data {
 	struct kvm_pgtable_walker	*walker;
 
 	const u64			start;
 	u64				addr;
 	const u64			end;
 };
 
+/* Positive walker return values point levels to skip */
+enum walker_return{
+	SKIP_CHILDREN = 1,
+	SKIP_SIBLINGS
+};
+
 static bool kvm_pgtable_walk_skip_bbm_tlbi(const struct kvm_pgtable_visit_ctx *ctx)
 {
 	return unlikely(ctx->flags & KVM_PGTABLE_WALK_SKIP_BBM_TLBI);
 }
 
 static bool kvm_pgtable_walk_skip_cmo(const struct kvm_pgtable_visit_ctx *ctx)
 {
 	return unlikely(ctx->flags & KVM_PGTABLE_WALK_SKIP_CMO);
 }
 
@@ -134,21 +140,21 @@ static bool kvm_pgtable_walk_continue(const struct kvm_pgtable_walker *walker,
 	 * update a PTE. In the context of a fault handler this is interpreted
 	 * as a signal to retry guest execution.
 	 *
 	 * Ignore the return code altogether for walkers outside a fault handler
 	 * (e.g. write protecting a range of memory) and chug along with the
 	 * page table walk.
 	 */
 	if (r == -EAGAIN)
 		return walker->flags & KVM_PGTABLE_WALK_IGNORE_EAGAIN;
 
-	return !r;
+	return r >= 0;
 }
 
 static int __kvm_pgtable_walk(struct kvm_pgtable_walk_data *data,
 			      struct kvm_pgtable_mm_ops *mm_ops, kvm_pteref_t pgtable, s8 level);
 
 static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 				      struct kvm_pgtable_mm_ops *mm_ops,
 				      kvm_pteref_t pteref, s8 level)
 {
 	enum kvm_pgtable_walk_flags flags = data->walker->flags;
@@ -185,23 +191,29 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
 	 * into a newly installed or replaced table.
 	 */
 	if (reload) {
 		ctx.old = READ_ONCE(*ptep);
 		table = kvm_pte_table(ctx.old, level);
 	}
 
 	if (!kvm_pgtable_walk_continue(data->walker, ret))
 		goto out;
 
-	if (!table) {
-		data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level));
-		data->addr += kvm_granule_size(level);
+	if (!table || ret >= SKIP_CHILDREN) {
+		u64 size;
+
+		if (ret == SKIP_SIBLINGS)	/* Skip siblings */
+			size = kvm_granule_size(level - 1);
+		else				/* Skip children */
+			size = kvm_granule_size(level);
+
+		data->addr = ALIGN_DOWN(data->addr, size) + size;
 		goto out;
 	}
 
 	childp = (kvm_pteref_t)kvm_pte_follow(ctx.old, mm_ops);
 	ret = __kvm_pgtable_walk(data, mm_ops, childp, level + 1);
 	if (!kvm_pgtable_walk_continue(data->walker, ret))
 		goto out;
 
 	if (ctx.flags & KVM_PGTABLE_WALK_TABLE_POST)
 		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_POST);
-- 
2.54.0