xen: introduce a new way to setup event channel upcall

The main differences with the currently implemented method are:

 - Requires a local APIC EOI, since it doesn't bypass the local APIC
   as the previous method used to do.
 - Can be set to use different IDT vectors on each vCPU. Note that
   FreeBSD doesn't make use of this feature since the event channel
   IDT vector is reserved system wide.

Note that the old method of setting the event channel upcall is
not removed, and will be used as a fallback if this newly introduced
method is not available.

MFC after:	1 month
Sponsored by:	Citrix Systems R&D

sys/x86/xen/hvm.c

@@ -51,6 +51,7 @@ __FBSDID("$FreeBSD$");
 #include <x86/apicreg.h>
 
 #include <xen/xen-os.h>
+#include <xen/error.h>
 #include <xen/features.h>
 #include <xen/gnttab.h>
 #include <xen/hypervisor.h>
@@ -88,6 +89,12 @@ int xen_vector_callback_enabled;
  */
 uint32_t hvm_start_flags;
 
+/**
+ * Signal whether the vector injected for the event channel upcall requires to
+ * be EOI'ed on the local APIC.
+ */
+bool xen_evtchn_needs_ack;
+
 /*------------------------------- Per-CPU Data -------------------------------*/
 DPCPU_DEFINE(struct vcpu_info, vcpu_local_info);
 DPCPU_DEFINE(struct vcpu_info *, vcpu_info);
@@ -223,6 +230,19 @@ xen_hvm_init_shared_info_page(void)
 		panic("HYPERVISOR_memory_op failed");
 }
 
+static int
+set_percpu_callback(unsigned int vcpu)
+{
+	struct xen_hvm_evtchn_upcall_vector vec;
+	int error;
+
+	vec.vcpu = vcpu;
+	vec.vector = IDT_EVTCHN;
+	error = HYPERVISOR_hvm_op(HVMOP_set_evtchn_upcall_vector, &vec);
+
+	return (error != 0 ? xen_translate_error(error) : 0);
+}
+
 /*
  * Tell the hypervisor how to contact us for event channel callbacks.
  */
@@ -240,12 +260,20 @@ xen_hvm_set_callback(device_t dev)
 	if (xen_feature(XENFEAT_hvm_callback_vector) != 0) {
 		int error;
 
-		xhp.value = HVM_CALLBACK_VECTOR(IDT_EVTCHN);
+		error = set_percpu_callback(0);
+		if (error == 0) {
+			xen_evtchn_needs_ack = true;
+			/* Trick toolstack to think we are enlightened */
+			xhp.value = 1;
+		} else
+			xhp.value = HVM_CALLBACK_VECTOR(IDT_EVTCHN);
 		error = HYPERVISOR_hvm_op(HVMOP_set_param, &xhp);
 		if (error == 0) {
 			xen_vector_callback_enabled = 1;
 			return;
-		}
+		} else if (xen_evtchn_needs_ack)
+			panic("Unable to setup fake HVM param: %d", error);
+
 		printf("Xen HVM callback vector registration failed (%d). "
 		    "Falling back to emulated device interrupt\n", error);
 	}
@@ -360,6 +388,7 @@ xen_hvm_init(enum xen_hvm_init_type init_type)
 	}
 
 	xen_vector_callback_enabled = 0;
+	xen_evtchn_needs_ack = false;
 	xen_hvm_set_callback(NULL);
 
 	/*
@@ -427,6 +456,20 @@ xen_hvm_cpu_init(void)
 	PCPU_SET(vcpu_id, (regs[0] & XEN_HVM_CPUID_VCPU_ID_PRESENT) ?
 	    regs[1] : PCPU_GET(acpi_id));
 
+	if (xen_evtchn_needs_ack && !IS_BSP()) {
+		/*
+		 * Setup the per-vpcu event channel upcall vector. This is only
+		 * required when using the new HVMOP_set_evtchn_upcall_vector
+		 * hypercall, which allows using a different vector for each
+		 * vCPU. Note that FreeBSD uses the same vector for all vCPUs
+		 * because it's not dynamically allocated.
+		 */
+		rc = set_percpu_callback(PCPU_GET(vcpu_id));
+		if (rc != 0)
+			panic("Event channel upcall vector setup failed: %d",
+			    rc);
+	}
+
 	/*
 	 * Set the vCPU info.
 	 *

sys/x86/xen/xen_intr.c

@@ -60,6 +60,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/xen/xen-os.h>
 
 #include <xen/xen-os.h>
+#include <xen/hvm.h>
 #include <xen/hypervisor.h>
 #include <xen/xen_intr.h>
 #include <xen/evtchn/evtchnvar.h>
@@ -620,6 +621,10 @@ xen_intr_handle_upcall(struct trapframe *trap_frame)
 			l1 &= ~(1UL << l1i);
 		}
 	}
+
+	if (xen_evtchn_needs_ack)
+		lapic_eoi();
+
 	critical_exit();
 }
 

sys/xen/hvm.h

@@ -104,5 +104,6 @@ void xen_hvm_suspend(void);
 void xen_hvm_resume(bool suspend_cancelled);
 
 extern uint32_t hvm_start_flags;
+extern bool xen_evtchn_needs_ack;
 
 #endif	/* __XEN_HVM_H__ */