[PATCH 2/9] KVM: arm64: Add helper for creating removed stage2 subtrees

[Ricardo Koller <ricarkol@google.com>]

Add a stage2 helper, kvm_pgtable_stage2_create_removed(), for creating
removed tables (the opposite of kvm_pgtable_stage2_free_removed()).
Creating a removed table is useful for splitting block PTEs into
subtrees of 4K PTEs.  For example, a 1G block PTE can be split into 4K
PTEs by first creating a fully populated tree, and then use it to
replace the 1G PTE in a single step.  This will be used in a
subsequent commit for eager huge-page splitting (a dirty-logging
optimization).

No functional change intended. This new function will be used in a
subsequent commit.

Signed-off-by: Ricardo Koller <ricarkol@google.com>
---
 arch/arm64/include/asm/kvm_pgtable.h | 25 +++++++++++++++
 arch/arm64/kvm/hyp/pgtable.c         | 47 ++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 84a271647007..8ad78d61af7f 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -450,6 +450,31 @@ void kvm_pgtable_stage2_destroy(struct kvm_pgtable *pgt);
  */
 void kvm_pgtable_stage2_free_removed(struct kvm_pgtable_mm_ops *mm_ops, void *pgtable, u32 level);
 
+/**
+ * kvm_pgtable_stage2_free_removed() - Create a removed stage-2 paging structure.
+ * @pgt:	Page-table structure initialised by kvm_pgtable_stage2_init*().
+ * @new:	Unlinked stage-2 paging structure to be created.
+ * @phys:	Physical address of the memory to map.
+ * @level:	Level of the stage-2 paging structure to be created.
+ * @prot:	Permissions and attributes for the mapping.
+ * @mc:		Cache of pre-allocated and zeroed memory from which to allocate
+ *		page-table pages.
+ *
+ * Create a removed page-table tree of PAGE_SIZE leaf PTEs under *new.
+ * This new page-table tree is not reachable (i.e., it is removed) from the
+ * root pgd and it's therefore unreachableby the hardware page-table
+ * walker. No TLB invalidation or CMOs are performed.
+ *
+ * If device attributes are not explicitly requested in @prot, then the
+ * mapping will be normal, cacheable.
+ *
+ * Return: 0 only if a fully populated tree was created, negative error
+ * code on failure. No partially-populated table can be returned.
+ */
+int kvm_pgtable_stage2_create_removed(struct kvm_pgtable *pgt,
+				      kvm_pte_t *new, u64 phys, u32 level,
+				      enum kvm_pgtable_prot prot, void *mc);
+
 /**
  * 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 87fd40d09056..0dee13007776 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1181,6 +1181,53 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size)
 	return kvm_pgtable_walk(pgt, addr, size, &walker);
 }
 
+/*
+ * map_data->force_pte is true in order to force creating PAGE_SIZE PTEs.
+ * data->addr is 0 because the IPA is irrelevant for a removed table.
+ */
+int kvm_pgtable_stage2_create_removed(struct kvm_pgtable *pgt,
+				      kvm_pte_t *new, u64 phys, u32 level,
+				      enum kvm_pgtable_prot prot, void *mc)
+{
+	struct stage2_map_data map_data = {
+		.phys		= phys,
+		.mmu		= pgt->mmu,
+		.memcache	= mc,
+		.force_pte	= true,
+	};
+	struct kvm_pgtable_walker walker = {
+		.cb		= stage2_map_walker,
+		.flags		= KVM_PGTABLE_WALK_LEAF |
+				  KVM_PGTABLE_WALK_REMOVED,
+		.arg		= &map_data,
+	};
+	struct kvm_pgtable_walk_data data = {
+		.walker	= &walker,
+		.addr	= 0,
+		.end	= kvm_granule_size(level),
+	};
+	struct kvm_pgtable_mm_ops *mm_ops = pgt->mm_ops;
+	kvm_pte_t *pgtable;
+	int ret;
+
+	ret = stage2_set_prot_attr(pgt, prot, &map_data.attr);
+	if (ret)
+		return ret;
+
+	pgtable = mm_ops->zalloc_page(mc);
+	if (!pgtable)
+		return -ENOMEM;
+
+	ret = __kvm_pgtable_walk(&data, mm_ops, pgtable, level + 1);
+	if (ret) {
+		kvm_pgtable_stage2_free_removed(mm_ops, pgtable, level);
+		mm_ops->put_page(pgtable);
+		return ret;
+	}
+
+	*new = kvm_init_table_pte(pgtable, mm_ops);
+	return 0;
+}
 
 int __kvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
 			      struct kvm_pgtable_mm_ops *mm_ops,
-- 
2.39.0.314.g84b9a713c41-goog