[PATCH 1/3] KVM: arm64: Prevent teardown finalisation of referenced 'hyp_vm'

[Will Deacon]

Destroying a 'hyp_vm' with an elevated referenced count in
__pkvm_finalize_teardown_vm() is only going to lead to tears.

In preparation for allowing limited references to be acquired on dying
VMs during the teardown process, factor out the handle-to-vm logic for
the teardown path and reuse it for both the 'start' and 'finalise'
stages of the teardown process.

Signed-off-by: Will Deacon <will at kernel.org>
---
 arch/arm64/kvm/hyp/nvhe/pkvm.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 8b906217c4c3..3fd3b930beeb 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -936,20 +936,27 @@ int __pkvm_reclaim_dying_guest_page(pkvm_handle_t handle, u64 gfn)
 	return ret;
 }
 
+static struct pkvm_hyp_vm *get_pkvm_unref_hyp_vm_locked(pkvm_handle_t handle)
+{
+	struct pkvm_hyp_vm *hyp_vm;
+
+	hyp_assert_lock_held(&vm_table_lock);
+
+	hyp_vm = get_vm_by_handle(handle);
+	if (!hyp_vm || hyp_page_count(hyp_vm))
+		return NULL;
+
+	return hyp_vm;
+}
+
 int __pkvm_start_teardown_vm(pkvm_handle_t handle)
 {
 	struct pkvm_hyp_vm *hyp_vm;
 	int ret = 0;
 
 	hyp_spin_lock(&vm_table_lock);
-	hyp_vm = get_vm_by_handle(handle);
-	if (!hyp_vm) {
-		ret = -ENOENT;
-		goto unlock;
-	} else if (WARN_ON(hyp_page_count(hyp_vm))) {
-		ret = -EBUSY;
-		goto unlock;
-	} else if (hyp_vm->kvm.arch.pkvm.is_dying) {
+	hyp_vm = get_pkvm_unref_hyp_vm_locked(handle);
+	if (!hyp_vm || hyp_vm->kvm.arch.pkvm.is_dying) {
 		ret = -EINVAL;
 		goto unlock;
 	}
@@ -971,12 +978,9 @@ int __pkvm_finalize_teardown_vm(pkvm_handle_t handle)
 	int err;
 
 	hyp_spin_lock(&vm_table_lock);
-	hyp_vm = get_vm_by_handle(handle);
-	if (!hyp_vm) {
-		err = -ENOENT;
-		goto err_unlock;
-	} else if (!hyp_vm->kvm.arch.pkvm.is_dying) {
-		err = -EBUSY;
+	hyp_vm = get_pkvm_unref_hyp_vm_locked(handle);
+	if (!hyp_vm || !hyp_vm->kvm.arch.pkvm.is_dying) {
+		err = -EINVAL;
 		goto err_unlock;
 	}
 
-- 
2.53.0.1118.gaef5881109-goog