KVM: PPC: Book3S HV: Tunable to disable KVM IRQ bypass

Add a  module parameter kvm_irq_bypass for kvm_hv.ko to
disable IRQ bypass for passthrough interrupts. The default
value of this tunable is 1 - that is enable the feature.

Since the tunable is used by built-in kernel code, we use
the module_param_cb macro to achieve this.
Signed-off-by: Suresh Warrier <warrier@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/include/asm/kvm_book3s.h

@@ -227,6 +227,7 @@ extern void kvmppc_copy_to_svcpu(struct kvmppc_book3s_shadow_vcpu *svcpu,
 				 struct kvm_vcpu *vcpu);
 extern void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu,
 				   struct kvmppc_book3s_shadow_vcpu *svcpu);
+extern int kvm_irq_bypass;
 
 static inline struct kvmppc_vcpu_book3s *to_book3s(struct kvm_vcpu *vcpu)
 {

arch/powerpc/include/asm/kvm_ppc.h

@@ -461,7 +461,7 @@ static inline int kvmppc_xics_enabled(struct kvm_vcpu *vcpu)
 static inline struct kvmppc_passthru_irqmap *kvmppc_get_passthru_irqmap(
 				struct kvm *kvm)
 {
-	if (kvm)
+	if (kvm && kvm_irq_bypass)
 		return kvm->arch.pimap;
 	return NULL;
 }

arch/powerpc/kvm/book3s_hv.c

@@ -95,6 +95,10 @@ static struct kernel_param_ops module_param_ops = {
 	.get = param_get_int,
 };
 
+module_param_cb(kvm_irq_bypass, &module_param_ops, &kvm_irq_bypass,
+							S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(kvm_irq_bypass, "Bypass passthrough interrupt optimization");
+
 module_param_cb(h_ipi_redirect, &module_param_ops, &h_ipi_redirect,
 							S_IRUGO | S_IWUSR);
 MODULE_PARM_DESC(h_ipi_redirect, "Redirect H_IPI wakeup to a free host core");
@@ -3443,6 +3447,9 @@ static int kvmppc_set_passthru_irq(struct kvm *kvm, int host_irq, int guest_gsi)
 	struct irq_chip *chip;
 	int i;
 
+	if (!kvm_irq_bypass)
+		return 1;
+
 	desc = irq_to_desc(host_irq);
 	if (!desc)
 		return -EIO;
@@ -3519,6 +3526,9 @@ static int kvmppc_clr_passthru_irq(struct kvm *kvm, int host_irq, int guest_gsi)
 	struct kvmppc_passthru_irqmap *pimap;
 	int i;
 
+	if (!kvm_irq_bypass)
+		return 0;
+
 	desc = irq_to_desc(host_irq);
 	if (!desc)
 		return -EIO;

arch/powerpc/kvm/book3s_hv_rm_xics.c

@@ -27,6 +27,8 @@
 
 int h_ipi_redirect = 1;
 EXPORT_SYMBOL(h_ipi_redirect);
+int kvm_irq_bypass = 1;
+EXPORT_SYMBOL(kvm_irq_bypass);
 
 static void icp_rm_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 			    u32 new_irq);