i386/xen: implement HYPERVISOR_vcpu_op

This is simply when guest tries to register a vcpu_info
and since vcpu_info placement is optional in the minimum ABI
therefore we can just fail with -ENOSYS

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

target/i386/kvm/xen-emu.c

@@ -27,6 +27,7 @@
 #include "hw/xen/interface/sched.h"
 #include "hw/xen/interface/memory.h"
 #include "hw/xen/interface/hvm/hvm_op.h"
+#include "hw/xen/interface/vcpu.h"
 
 #include "xen-compat.h"
 
@@ -363,6 +364,25 @@ static bool kvm_xen_hcall_hvm_op(struct kvm_xen_exit *exit, X86CPU *cpu,
     }
 }
 
+static bool kvm_xen_hcall_vcpu_op(struct kvm_xen_exit *exit, X86CPU *cpu,
+                                  int cmd, int vcpu_id, uint64_t arg)
+{
+    int err;
+
+    switch (cmd) {
+    case VCPUOP_register_vcpu_info:
+        /* no vcpu info placement for now */
+        err = -ENOSYS;
+        break;
+
+    default:
+        return false;
+    }
+
+    exit->u.hcall.result = err;
+    return true;
+}
+
 int kvm_xen_soft_reset(void)
 {
     int err;
@@ -464,6 +484,11 @@ static bool do_kvm_xen_handle_exit(X86CPU *cpu, struct kvm_xen_exit *exit)
     case __HYPERVISOR_sched_op:
         return kvm_xen_hcall_sched_op(exit, cpu, exit->u.hcall.params[0],
                                       exit->u.hcall.params[1]);
+    case __HYPERVISOR_vcpu_op:
+        return kvm_xen_hcall_vcpu_op(exit, cpu,
+                                     exit->u.hcall.params[0],
+                                     exit->u.hcall.params[1],
+                                     exit->u.hcall.params[2]);
     case __HYPERVISOR_hvm_op:
         return kvm_xen_hcall_hvm_op(exit, cpu, exit->u.hcall.params[0],
                                     exit->u.hcall.params[1]);