[PATCH 01/14] KVM: arm64: Add a helper to tear down unlinked stage-2 subtrees

[Oliver Upton]

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 at linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h | 11 +++++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 26 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 9f339dffbc1a..d71fb92dc913 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -316,6 +316,17 @@ int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
  */
 void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
 
+/**
+ * kvm_pgtable_stage2_free_removed() - Free a removed stage-2 paging structure.
+ * @pgtable:	Unlinked stage-2 paging structure to be freed.
+ * @level:	Level of the stage-2 paging structure to be freed.
+ * @arg:	Page-table structure initialised by kvm_pgtable_stage2_init*()
+ *
+ * The page-table is assumed to be unreachable by any hardware walkers prior to
+ * freeing and therefore no TLB invalidation is performed.
+ */
+void kvm_pgtable_stage2_free_removed(void *pgtable, u32 level, void *arg);
+
 /**
  * kvm_pgtable_stage2_map() - Install a mapping in a guest stage-2 page-table.
  * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init*().
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 2cb3867eb7c2..d8127c25424c 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1233,3 +1233,29 @@ 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(void *pgtable, u32 level, void *arg)
+{
+	struct kvm_pgtable *pgt = (struct kvm_pgtable *)arg;
+	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,
+		.arg	= pgt->mm_ops,
+	};
+	struct kvm_pgtable_walk_data data = {
+		.pgt	= pgt,
+		.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, ptep, level));
+}
-- 
2.37.2.672.g94769d06f0-goog