KVM: arm64: Use mtree_empty() to determine if SMCCC filter configured

The smccc_filter maple tree is only populated if userspace attempted to
configure it. Use the state of the maple tree to determine if the filter
has been configured, eliminating the VM flag.
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231004234947.207507-4-oliver.upton@linux.devSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/include/asm/kvm_host.h

@@ -239,10 +239,8 @@ struct kvm_arch {
 #define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			5
 	/* Timer PPIs made immutable */
 #define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
-	/* SMCCC filter initialized for the VM */
-#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED		7
 	/* Initial ID reg values loaded */
-#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		8
+#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
 	unsigned long flags;
 
 	/* VM-wide vCPU feature set */

arch/arm64/kvm/hypercalls.c

@@ -164,7 +164,7 @@ static int kvm_smccc_filter_insert_reserved(struct kvm *kvm)
 
 static bool kvm_smccc_filter_configured(struct kvm *kvm)
 {
-	return test_bit(KVM_ARCH_FLAT_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags);
+	return !mtree_empty(&kvm->arch.smccc_filter);
 }
 
 static int kvm_smccc_set_filter(struct kvm *kvm, struct kvm_smccc_filter __user *uaddr)
@@ -201,11 +201,6 @@ static int kvm_smccc_set_filter(struct kvm *kvm, struct kvm_smccc_filter __user
 
 	r = mtree_insert_range(&kvm->arch.smccc_filter, start, end,
 			       xa_mk_value(filter.action), GFP_KERNEL_ACCOUNT);
-	if (r)
-		goto out_unlock;
-
-	set_bit(KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags);
-
 out_unlock:
 	mutex_unlock(&kvm->arch.config_lock);
 	return r;