configs: Add --kvm-userspace-gic to fs_bigLITTLE.py

This will allow a user to select gem5 simulation of the GIC via
command line; Necessary option when the simulated GIC != than the
host GIC

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: I30e151b774ddfa7f4e91054a375254e15007af3f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/44006
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Richard Cooper <richard.cooper@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/example/arm/fs_bigLITTLE.py

@@ -197,6 +197,9 @@ def addOptions(parser):
                         help="Custom Linux kernel command")
     parser.add_argument("--bootloader", action="append",
                         help="executable file that runs before the --kernel")
+    parser.add_argument("--kvm-userspace-gic", action="store_true",
+                        default=False,
+                        help="Use the gem5 GIC in a KVM simulation")
     parser.add_argument("-P", "--param", action="append", default=[],
         help="Set a SimObject parameter relative to the root node. "
              "An extended Python multi range slicing syntax can be used "
@@ -281,7 +284,7 @@ def build(options):
 
     # Create a KVM VM and do KVM-specific configuration
     if issubclass(big_model, KvmCluster):
-        _build_kvm(system, all_cpus)
+        _build_kvm(options, system, all_cpus)
 
     # Linux device tree
     if options.dtb is not None:
@@ -305,9 +308,18 @@ def build(options):
 
     return root
 
-def _build_kvm(system, cpus):
+def _build_kvm(options, system, cpus):
     system.kvm_vm = KvmVM()
 
+    if options.kvm_userspace_gic:
+        # We will use the simulated GIC.
+        # In order to make it work we need to remove the system interface
+        # of the generic timer from the DTB and we need to inform the
+        # MuxingKvmGic class to use the gem5 GIC instead of relying on the
+        # host interrupt controller
+        GenericTimer.generateDeviceTree = SimObject.generateDeviceTree
+        system.realview.gic.simulate_gic = True
+
     # Assign KVM CPUs to their own event queues / threads. This
     # has to be done after creating caches and other child objects
     # since these mustn't inherit the CPU event queue.