[PATCH v2 3/3] KVM: arm64: Make stage2_split_walker() skip unnecessary walks

[Leonardo Bras]

Currently, when splitting, all the child and sibling nodes will be walked,
with the walker just returning earlier if there is nothing to do. This
means all pagetable entries in the splitting range get a callback from the
walker function, even if it was a level-3 entry.

Optimize splitting by skipping all level-3 entries, as they are already the
smallest block size and can't be split any further.
(i.e. set flag KVM_PGTABLE_WALK_SKIP_LEVEL3)

kvm_mmu_split_huge_pages called in
	kvm_clear_dirty_log_protect() - manual - 64-page granularity
	kvm_mmu_split_memory_region() - no manual - all memory

Signed-off-by: Leonardo Bras <leo.bras@xxxxxxx>
---
 arch/arm64/kvm/hyp/pgtable.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b9a2078efc51..9ae4d9d7ed56 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1565,21 +1565,22 @@ static int stage2_split_walker(const struct kvm_pgtable_visit_ctx *ctx,
 	new = kvm_init_table_pte(childp, mm_ops);
 	stage2_make_pte(ctx, new);
 	return 0;
 }
 
 int kvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
 			     struct kvm_mmu_memory_cache *mc)
 {
 	struct kvm_pgtable_walker walker = {
 		.cb	= stage2_split_walker,
-		.flags	= KVM_PGTABLE_WALK_LEAF,
+		.flags	= KVM_PGTABLE_WALK_LEAF |
+			  KVM_PGTABLE_WALK_SKIP_LEVEL3,
 		.arg	= mc,
 	};
 	int ret;
 
 	ret = kvm_pgtable_walk(pgt, addr, size, &walker);
 	dsb(ishst);
 	return ret;
 }
 
 int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
-- 
2.54.0