KVM: arm64: Adjust partial code of hyp stage-1 map and guest stage-2 map

Procedures of hyp stage-1 map and guest stage-2 map are quite different,
but they are tied closely by function kvm_set_valid_leaf_pte().
So adjust the relative code for ease of code maintenance in the future.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210114121350.123684-2-wangyanan55@huawei.com

arch/arm64/kvm/hyp/pgtable.c

@@ -170,10 +170,9 @@ static void kvm_set_table_pte(kvm_pte_t *ptep, kvm_pte_t *childp)
 	smp_store_release(ptep, pte);
 }
 
-static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr,
-				   u32 level)
+static kvm_pte_t kvm_init_valid_leaf_pte(u64 pa, kvm_pte_t attr, u32 level)
 {
-	kvm_pte_t old = *ptep, pte = kvm_phys_to_pte(pa);
+	kvm_pte_t pte = kvm_phys_to_pte(pa);
 	u64 type = (level == KVM_PGTABLE_MAX_LEVELS - 1) ? KVM_PTE_TYPE_PAGE :
 							   KVM_PTE_TYPE_BLOCK;
 
@@ -181,12 +180,7 @@ static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr,
 	pte |= FIELD_PREP(KVM_PTE_TYPE, type);
 	pte |= KVM_PTE_VALID;
 
-	/* Tolerate KVM recreating the exact same mapping. */
-	if (kvm_pte_valid(old))
-		return old == pte;
-
-	smp_store_release(ptep, pte);
-	return true;
+	return pte;
 }
 
 static int kvm_pgtable_visitor_cb(struct kvm_pgtable_walk_data *data, u64 addr,
@@ -341,12 +335,17 @@ static int hyp_map_set_prot_attr(enum kvm_pgtable_prot prot,
 static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 				    kvm_pte_t *ptep, struct hyp_map_data *data)
 {
+	kvm_pte_t new, old = *ptep;
 	u64 granule = kvm_granule_size(level), phys = data->phys;
 
 	if (!kvm_block_mapping_supported(addr, end, phys, level))
 		return false;
 
-	WARN_ON(!kvm_set_valid_leaf_pte(ptep, phys, data->attr, level));
+	/* Tolerate KVM recreating the exact same mapping */
+	new = kvm_init_valid_leaf_pte(phys, data->attr, level);
+	if (old != new && !WARN_ON(kvm_pte_valid(old)))
+		smp_store_release(ptep, new);
+
 	data->phys += granule;
 	return true;
 }
@@ -465,27 +464,30 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 				       kvm_pte_t *ptep,
 				       struct stage2_map_data *data)
 {
+	kvm_pte_t new, old = *ptep;
 	u64 granule = kvm_granule_size(level), phys = data->phys;
+	struct page *page = virt_to_page(ptep);
 
 	if (!kvm_block_mapping_supported(addr, end, phys, level))
 		return false;
 
-	/*
-	 * If the PTE was already valid, drop the refcount on the table
-	 * early, as it will be bumped-up again in stage2_map_walk_leaf().
-	 * This ensures that the refcount stays constant across a valid to
-	 * valid PTE update.
-	 */
-	if (kvm_pte_valid(*ptep))
-		put_page(virt_to_page(ptep));
-
-	if (kvm_set_valid_leaf_pte(ptep, phys, data->attr, level))
+	new = kvm_init_valid_leaf_pte(phys, data->attr, level);
+	if (kvm_pte_valid(old)) {
+		/* Tolerate KVM recreating the exact same mapping */
+		if (old == new)
 			goto out;
 
-	/* There's an existing valid leaf entry, so perform break-before-make */
+		/*
+		 * There's an existing different valid leaf entry, so perform
+		 * break-before-make.
+		 */
 		kvm_set_invalid_pte(ptep);
 		kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
-	kvm_set_valid_leaf_pte(ptep, phys, data->attr, level);
+		put_page(page);
+	}
+
+	smp_store_release(ptep, new);
+	get_page(page);
 out:
 	data->phys += granule;
 	return true;
@@ -527,7 +529,7 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	}
 
 	if (stage2_map_walker_try_leaf(addr, end, level, ptep, data))
-		goto out_get_page;
+		return 0;
 
 	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
@@ -551,9 +553,8 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	}
 
 	kvm_set_table_pte(ptep, childp);
-
-out_get_page:
 	get_page(page);
+
 	return 0;
 }