KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees

A subsequent change to KVM will move the tear down of an unlinked
stage-2 subtree out of the critical path of the break-before-make
sequence.

Introduce a new helper for tearing down unlinked stage-2 subtrees.
Leverage the existing stage-2 free walkers to do so, with a deep call
into __kvm_pgtable_walk() as the subtree is no longer reachable from the
root.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221107215644.1895162-6-oliver.upton@linux.dev

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 93989b750a26..363a5cce7e1a 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1203,3 +1203,26 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt)
 	pgt->mm_ops->free_pages_exact(pgt->pgd, pgd_sz);
 	pgt->pgd = NULL;
 }
+
+void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level)
+{
+	kvm_pte_t *ptep = (kvm_pte_t *)pgtable;
+	struct kvm_pgtable_walker walker = {
+		.cb	= stage2_free_walker,
+		.flags	= KVM_PGTABLE_WALK_LEAF |
+			  KVM_PGTABLE_WALK_TABLE_POST,
+	};
+	struct kvm_pgtable_walk_data data = {
+		.walker	= &walker,
+
+		/*
+		 * At this point the IPA really doesn't matter, as the page
+		 * table being traversed has already been removed from the stage
+		 * 2. Set an appropriate range to cover the entire page table.
+		 */
+		.addr	= 0,
+		.end	= kvm_granule_size(level),
+	};
+
+	WARN_ON(__kvm_pgtable_walk(&data, mm_ops, ptep, level));
+}