[PATCH 02/20] KVM: arm64: Propagate host stage-2 annotated entries on block split

[Vincent Donnefort]

Propagate ownership refcounts for invalid stage-2 entries mapped on
block split. This intends to allow splitting host stage-2 blocks while
keeping existing page ownership and metadata annotations.

Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 34f78a58cded..0ca157ecee64 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1033,15 +1033,28 @@ static int stage2_map_walk_table_pre(const struct kvm_pgtable_visit_ctx *ctx,
 static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t *ptep)
 {
 	kvm_pte_t block_pte = ctx->old;
+	bool counted, valid;
 	u64 pa;
 	int i;
 
-	if (!kvm_pte_valid(block_pte))
+	counted = stage2_pte_is_counted(block_pte);
+	valid = kvm_pte_valid(block_pte);
+
+	if (!valid && !counted)
+		return;
+
+	/*
+	 * Shared walks not supported: cannot rollback refcounts on break
+	 * failure.
+	 */
+	if (counted && WARN_ON_ONCE(kvm_pgtable_walk_shared(ctx)))
 		return;
 
 	pa = ALIGN_DOWN(ctx->addr, kvm_granule_size(ctx->level));
 	for (i = 0; i < PTRS_PER_PTE; ++i, ++ptep, pa += kvm_granule_size(ctx->level + 1)) {
-		kvm_pte_t pte = kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1);
+		kvm_pte_t pte = valid ?
+			kvm_init_valid_leaf_pte(pa, block_pte, ctx->level + 1) :
+			block_pte;
 
 		/*
 		 * Skip ptes in the range being modified by the caller if we're
@@ -1053,8 +1066,11 @@ static void stage2_map_prefault_idmap(const struct kvm_pgtable_visit_ctx *ctx, k
 		 * that should happen very infrequently.
 		 */
 		if ((ctx->level < (KVM_PGTABLE_LAST_LEVEL - 1)) ||
-		    (pa < ctx->addr) || (pa >= ctx->end))
+		    (pa < ctx->addr) || (pa >= ctx->end)) {
 			*ptep = pte;
+			if (counted)
+				ctx->mm_ops->get_page(ptep);
+		}
 	}
 }
 
-- 
2.55.0.508.g3f0d502094-goog