KVM: arm64: Do arm/arch initialization without bouncing through kvm_init()

Do arm/arch specific initialization directly in arm's module_init(), now
called kvm_arm_init(), instead of bouncing through kvm_init() to reach
kvm_arch_init().  Invoking kvm_arch_init() is the very first action
performed by kvm_init(), so from a initialization perspective this is a
glorified nop.

Avoiding kvm_arch_init() also fixes a mostly benign bug as kvm_arch_exit()
doesn't properly unwind if a later stage of kvm_init() fails.  While the
soon-to-be-deleted comment about compiling as a module being unsupported
is correct, kvm_arch_exit() can still be called by kvm_init() if any step
after the call to kvm_arch_init() succeeds.

Add a FIXME to call out that pKVM initialization isn't unwound if
kvm_init() fails, which is a pre-existing problem inherited from
kvm_arch_exit().

Making kvm_arch_init() a nop will also allow dropping kvm_arch_init() and
kvm_arch_exit() entirely once all other architectures follow suit.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221130230934.1014142-20-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/arm64/kvm/arm.c

@@ -2207,7 +2207,7 @@ void kvm_arch_irq_bypass_start(struct irq_bypass_consumer *cons)
 /**
  * Initialize Hyp-mode and memory mappings on all CPUs.
  */
-int kvm_arch_init(void *opaque)
+int kvm_arm_init(void)
 {
 	int err;
 	bool in_hyp_mode;
@@ -2281,6 +2281,14 @@ int kvm_arch_init(void *opaque)
 		kvm_info("Hyp mode initialized successfully\n");
 	}
 
+	/*
+	 * FIXME: Do something reasonable if kvm_init() fails after pKVM
+	 * hypervisor protection is finalized.
+	 */
+	err = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
+	if (err)
+		goto out_subs;
+
 	return 0;
 
 out_subs:
@@ -2293,10 +2301,15 @@ int kvm_arch_init(void *opaque)
 	return err;
 }
 
+int kvm_arch_init(void *opaque)
+{
+	return 0;
+}
+
 /* NOP: Compiling as a module not supported */
 void kvm_arch_exit(void)
 {
-	kvm_unregister_perf_callbacks();
+
 }
 
 static int __init early_kvm_mode_cfg(char *arg)
@@ -2337,10 +2350,4 @@ enum kvm_mode kvm_get_mode(void)
 	return kvm_mode;
 }
 
-static int arm_init(void)
-{
-	int rc = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
-	return rc;
-}
-
-module_init(arm_init);
+module_init(kvm_arm_init);