KVM: arm64: vgic: Simplify kvm_vgic_destroy()

When destroying a vgic, we have rather cumbersome rules about
when slots_lock and config_lock are held, resulting in fun
buglets.

The first port of call is to simplify kvm_vgic_map_resources()
so that there is only one call to kvm_vgic_destroy() instead of
two, with the second only holding half of the locks.

For that, we kill the non-locking primitive and move the call
outside of the locking altogether. This doesn't change anything
(we re-acquire the locks and teardown the whole vgic), and
simplifies the code significantly.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20231207151201.3028710-2-maz@kernel.orgSigned-off-by: Oliver Upton <oliver.upton@linux.dev>

arch/arm64/kvm/vgic/vgic-init.c

@@ -382,26 +382,24 @@ void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
 	vgic_cpu->rd_iodev.base_addr = VGIC_ADDR_UNDEF;
 }
 
-static void __kvm_vgic_destroy(struct kvm *kvm)
+void kvm_vgic_destroy(struct kvm *kvm)
 {
 	struct kvm_vcpu *vcpu;
 	unsigned long i;
 
-	lockdep_assert_held(&kvm->arch.config_lock);
+	mutex_lock(&kvm->slots_lock);
 
 	vgic_debug_destroy(kvm);
 
 	kvm_for_each_vcpu(i, vcpu, kvm)
 		kvm_vgic_vcpu_destroy(vcpu);
 
+	mutex_lock(&kvm->arch.config_lock);
+
 	kvm_vgic_dist_destroy(kvm);
-}
 
-void kvm_vgic_destroy(struct kvm *kvm)
-{
-	mutex_lock(&kvm->arch.config_lock);
-	__kvm_vgic_destroy(kvm);
 	mutex_unlock(&kvm->arch.config_lock);
+	mutex_unlock(&kvm->slots_lock);
 }
 
 /**
@@ -469,25 +467,26 @@ int kvm_vgic_map_resources(struct kvm *kvm)
 		type = VGIC_V3;
 	}
 
-	if (ret) {
-		__kvm_vgic_destroy(kvm);
+	if (ret)
 		goto out;
-	}
+
 	dist->ready = true;
 	dist_base = dist->vgic_dist_base;
 	mutex_unlock(&kvm->arch.config_lock);
 
 	ret = vgic_register_dist_iodev(kvm, dist_base, type);
-	if (ret) {
+	if (ret)
 		kvm_err("Unable to register VGIC dist MMIO regions\n");
-		kvm_vgic_destroy(kvm);
-	}
-	mutex_unlock(&kvm->slots_lock);
-	return ret;
 
+	goto out_slots;
 out:
 	mutex_unlock(&kvm->arch.config_lock);
+out_slots:
 	mutex_unlock(&kvm->slots_lock);
+
+	if (ret)
+		kvm_vgic_destroy(kvm);
+
 	return ret;
 }