[PATCH v6 12/18] KVM: arm64: Move hyp_vm refcount into the structure

[Vincent Donnefort <vdonnefort@google.com>]

In preparation for allocating hyp_vm using the pKVM heap allocator
(hyp_alloc()), move its reference count out of the page metadata
(vmemmap) and place it into the structure itself. This transition is
necessary because hyp_alloc() allows multiple small objects to share the
same physical page.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/hyp/include/nvhe/pkvm.h | 13 +++++++++++++
 arch/arm64/kvm/hyp/nvhe/pkvm.c         | 10 +++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
index c1171451e1be..b208544141c0 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
@@ -42,6 +42,7 @@ struct pkvm_hyp_vm {
 	struct kvm_pgtable pgt;
 	struct kvm_pgtable_mm_ops mm_ops;
 	struct hyp_pool pool;
+	unsigned short refcount;
 	hyp_spinlock_t lock;
 
 	/* Array of the hyp vCPU structures for this VM. */
@@ -66,6 +67,18 @@ static inline bool pkvm_hyp_vm_is_protected(struct pkvm_hyp_vm *hyp_vm)
 	return kvm_vm_is_protected(&hyp_vm->kvm);
 }
 
+static inline void pkvm_hyp_vm_ref_inc(struct pkvm_hyp_vm *hyp_vm)
+{
+	BUG_ON(hyp_vm->refcount == USHRT_MAX);
+	hyp_vm->refcount++;
+}
+
+static inline void pkvm_hyp_vm_ref_dec(struct pkvm_hyp_vm *hyp_vm)
+{
+	BUG_ON(!hyp_vm->refcount);
+	hyp_vm->refcount--;
+}
+
 void pkvm_hyp_vm_table_init(void *tbl);
 
 int __pkvm_reserve_vm(void);
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 5cdb0318fa7b..98db5bd28dde 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -278,7 +278,7 @@ struct pkvm_hyp_vcpu *pkvm_load_hyp_vcpu(pkvm_handle_t handle,
 	}
 
 	hyp_vcpu->loaded_hyp_vcpu = this_cpu_ptr(&loaded_hyp_vcpu);
-	hyp_page_ref_inc(hyp_virt_to_page(hyp_vm));
+	pkvm_hyp_vm_ref_inc(hyp_vm);
 unlock:
 	hyp_spin_unlock(&vm_table_lock);
 
@@ -294,7 +294,7 @@ void pkvm_put_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 	hyp_spin_lock(&vm_table_lock);
 	hyp_vcpu->loaded_hyp_vcpu = NULL;
 	__this_cpu_write(loaded_hyp_vcpu, NULL);
-	hyp_page_ref_dec(hyp_virt_to_page(hyp_vm));
+	pkvm_hyp_vm_ref_dec(hyp_vm);
 	hyp_spin_unlock(&vm_table_lock);
 }
 
@@ -311,7 +311,7 @@ struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle)
 	hyp_spin_lock(&vm_table_lock);
 	hyp_vm = get_vm_by_handle(handle);
 	if (hyp_vm)
-		hyp_page_ref_inc(hyp_virt_to_page(hyp_vm));
+		pkvm_hyp_vm_ref_inc(hyp_vm);
 	hyp_spin_unlock(&vm_table_lock);
 
 	return hyp_vm;
@@ -320,7 +320,7 @@ struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle)
 void put_pkvm_hyp_vm(struct pkvm_hyp_vm *hyp_vm)
 {
 	hyp_spin_lock(&vm_table_lock);
-	hyp_page_ref_dec(hyp_virt_to_page(hyp_vm));
+	pkvm_hyp_vm_ref_dec(hyp_vm);
 	hyp_spin_unlock(&vm_table_lock);
 }
 
@@ -979,7 +979,7 @@ static struct pkvm_hyp_vm *get_pkvm_unref_hyp_vm_locked(pkvm_handle_t handle)
 	hyp_assert_lock_held(&vm_table_lock);
 
 	hyp_vm = get_vm_by_handle(handle);
-	if (!hyp_vm || hyp_page_count(hyp_vm))
+	if (!hyp_vm || hyp_vm->refcount)
 		return NULL;
 
 	return hyp_vm;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog