x86/xen: Split HVM vector callback setup and interrupt gate allocation

As a preparatory change for making alloc_intr_gate() __init split
xen_callback_vector() into callback vector setup via hypercall
(xen_setup_callback_vector()) and interrupt gate allocation
(xen_alloc_callback_vector()).

xen_setup_callback_vector() is being called twice: on init and upon
system resume from xen_hvm_post_suspend(). alloc_intr_gate() only
needs to be called once.
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200428093824.1451532-2-vkuznets@redhat.com

arch/x86/xen/suspend_hvm.c

@@ -13,6 +13,6 @@ void xen_hvm_post_suspend(int suspend_cancelled)
 		xen_hvm_init_shared_info();
 		xen_vcpu_restore();
 	}
-	xen_callback_vector();
+	xen_setup_callback_vector();
 	xen_unplug_emulated_devices();
 }

arch/x86/xen/xen-ops.h

@@ -55,7 +55,7 @@ void xen_enable_sysenter(void);
 void xen_enable_syscall(void);
 void xen_vcpu_restore(void);
 
-void xen_callback_vector(void);
+void xen_setup_callback_vector(void);
 void xen_hvm_init_shared_info(void);
 void xen_unplug_emulated_devices(void);
 

drivers/xen/events/events_base.c

@@ -1639,26 +1639,30 @@ EXPORT_SYMBOL_GPL(xen_set_callback_via);
 /* Vector callbacks are better than PCI interrupts to receive event
  * channel notifications because we can receive vector callbacks on any
  * vcpu and we don't need PCI support or APIC interactions. */
-void xen_callback_vector(void)
+void xen_setup_callback_vector(void)
 {
-	int rc;
 	uint64_t callback_via;
 
 	if (xen_have_vector_callback) {
 		callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
-		rc = xen_set_callback_via(callback_via);
-		if (rc) {
+		if (xen_set_callback_via(callback_via)) {
 			pr_err("Request for Xen HVM callback vector failed\n");
 			xen_have_vector_callback = 0;
-			return;
 		}
-		pr_info_once("Xen HVM callback vector for event delivery is enabled\n");
-		alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
-				xen_hvm_callback_vector);
 	}
 }
+
+static __init void xen_alloc_callback_vector(void)
+{
+	if (!xen_have_vector_callback)
+		return;
+
+	pr_info("Xen HVM callback vector for event delivery is enabled\n");
+	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, xen_hvm_callback_vector);
+}
 #else
-void xen_callback_vector(void) {}
+void xen_setup_callback_vector(void) {}
+static inline void xen_alloc_callback_vector(void) {}
 #endif
 
 #undef MODULE_PARAM_PREFIX
@@ -1692,8 +1696,10 @@ void __init xen_init_IRQ(void)
 		if (xen_initial_domain())
 			pci_xen_initial_domain();
 	}
-	if (xen_feature(XENFEAT_hvm_callback_vector))
-		xen_callback_vector();
+	if (xen_feature(XENFEAT_hvm_callback_vector)) {
+		xen_setup_callback_vector();
+		xen_alloc_callback_vector();
+	}
 
 	if (xen_hvm_domain()) {
 		native_init_IRQ();