[PATCH] KVM: Directly return result from kvm_arch_check_processor_compat()

[Sean Christopherson <sean.j.christopherson@intel.com>]

Add a wrapper to invoke kvm_arch_check_processor_compat() so that the
boilerplate ugliness of checking virtualization support on all CPUs is
hidden from the arch specific code.  x86's implementation in particular
is quite heinous, as it unnecessarily propagates the out-param pattern
into kvm_x86_ops.

While the x86 specific issue could be resolved solely by changing
kvm_x86_ops, make the change for all architectures as returning a value
directly is prettier and technically more robust, e.g. s390 doesn't set
the out param, which could lead to subtle breakage in the (highly
unlikely) scenario where the out-param was not pre-initialized by the
caller.

Opportunistically annotate svm_check_processor_compat() with __init.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---

Tested on VMX only.

 arch/mips/kvm/mips.c             | 4 ++--
 arch/powerpc/kvm/powerpc.c       | 4 ++--
 arch/s390/include/asm/kvm_host.h | 1 -
 arch/s390/kvm/kvm-s390.c         | 5 +++++
 arch/x86/include/asm/kvm_host.h  | 2 +-
 arch/x86/kvm/svm.c               | 4 ++--
 arch/x86/kvm/vmx/vmx.c           | 8 ++++----
 arch/x86/kvm/x86.c               | 4 ++--
 include/linux/kvm_host.h         | 2 +-
 virt/kvm/arm/arm.c               | 4 ++--
 virt/kvm/kvm_main.c              | 9 ++++++---
 11 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 6d0517ac18e5..1c22b938c550 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -123,9 +123,9 @@ int kvm_arch_hardware_setup(void)
 	return 0;
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void)
 {
-	*(int *)rtn = 0;
+	return 0;
 }
 
 int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 92910b7c5bcc..7b7635201739 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -425,9 +425,9 @@ int kvm_arch_hardware_setup(void)
 	return 0;
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void)
 {
-	*(int *)rtn = kvmppc_core_check_processor_compat();
+	return kvmppc_core_check_processor_compat();
 }
 
 int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index c47e22bba87f..96a1603ecf10 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -903,7 +903,6 @@ extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
 extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
 
 static inline void kvm_arch_hardware_disable(void) {}
-static inline void kvm_arch_check_processor_compat(void *rtn) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
 static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
 static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 28f35d2b06cb..4c50bd533ebc 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -221,6 +221,11 @@ int kvm_arch_hardware_enable(void)
 	return 0;
 }
 
+int kvm_arch_check_processor_compat(void)
+{
+	return 0;
+}
+
 static void kvm_gmap_notifier(struct gmap *gmap, unsigned long start,
 			      unsigned long end);
 
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 8d68ba0cba0c..02ba99ef8c5f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -995,7 +995,7 @@ struct kvm_x86_ops {
 	int (*disabled_by_bios)(void);             /* __init */
 	int (*hardware_enable)(void);
 	void (*hardware_disable)(void);
-	void (*check_processor_compatibility)(void *rtn);
+	int (*check_processor_compatibility)(void);/* __init */
 	int (*hardware_setup)(void);               /* __init */
 	void (*hardware_unsetup)(void);            /* __exit */
 	bool (*cpu_has_accelerated_tpr)(void);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 406b558abfef..236e2fc0edec 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5859,9 +5859,9 @@ svm_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
 	hypercall[2] = 0xd9;
 }
 
-static void svm_check_processor_compat(void *rtn)
+static int __init svm_check_processor_compat(void)
 {
-	*(int *)rtn = 0;
+	return 0;
 }
 
 static bool svm_cpu_has_accelerated_tpr(void)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d8f101b58ab8..7d0733b8f383 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6720,22 +6720,22 @@ static int vmx_vm_init(struct kvm *kvm)
 	return 0;
 }
 
-static void __init vmx_check_processor_compat(void *rtn)
+static int __init vmx_check_processor_compat(void)
 {
 	struct vmcs_config vmcs_conf;
 	struct vmx_capability vmx_cap;
 
-	*(int *)rtn = 0;
 	if (setup_vmcs_config(&vmcs_conf, &vmx_cap) < 0)
-		*(int *)rtn = -EIO;
+		return -EIO;
 	if (nested)
 		nested_vmx_setup_ctls_msrs(&vmcs_conf.nested, vmx_cap.ept,
 					   enable_apicv);
 	if (memcmp(&vmcs_config, &vmcs_conf, sizeof(struct vmcs_config)) != 0) {
 		printk(KERN_ERR "kvm: CPU %d feature inconsistency!\n",
 				smp_processor_id());
-		*(int *)rtn = -EIO;
+		return -EIO;
 	}
+	return 0;
 }
 
 static u64 vmx_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c09507057743..6214c27b0c2a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9042,9 +9042,9 @@ void kvm_arch_hardware_unsetup(void)
 	kvm_x86_ops->hardware_unsetup();
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void)
 {
-	kvm_x86_ops->check_processor_compatibility(rtn);
+	return kvm_x86_ops->check_processor_compatibility();
 }
 
 bool kvm_vcpu_is_reset_bsp(struct kvm_vcpu *vcpu)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 640a03642766..0ddef348b9b0 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -842,7 +842,7 @@ int kvm_arch_hardware_enable(void);
 void kvm_arch_hardware_disable(void);
 int kvm_arch_hardware_setup(void);
 void kvm_arch_hardware_unsetup(void);
-void kvm_arch_check_processor_compat(void *rtn);
+int kvm_arch_check_processor_compat(void);
 int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
 bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu);
 int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index be4ec5f3ba5f..67ecadbd8961 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -105,9 +105,9 @@ int kvm_arch_hardware_setup(void)
 	return 0;
 }
 
-void kvm_arch_check_processor_compat(void *rtn)
+int kvm_arch_check_processor_compat(void)
 {
-	*(int *)rtn = 0;
+	return 0;
 }
 
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 4bb20f2b2a69..41effae3f9ec 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4135,6 +4135,11 @@ static void kvm_sched_out(struct preempt_notifier *pn,
 	kvm_arch_vcpu_put(vcpu);
 }
 
+static void check_processor_compat(void *rtn)
+{
+	*(int *)rtn = kvm_arch_check_processor_compat();
+}
+
 int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 		  struct module *module)
 {
@@ -4166,9 +4171,7 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
 		goto out_free_0a;
 
 	for_each_online_cpu(cpu) {
-		smp_call_function_single(cpu,
-				kvm_arch_check_processor_compat,
-				&r, 1);
+		smp_call_function_single(cpu, check_processor_compat, &r, 1);
 		if (r < 0)
 			goto out_free_1;
 	}
-- 
2.21.0