stdlib: Add "is_kvm_core" function to AbstractCore

This function is useful in various parts of the stdlib to know if a core
is KVM or not as KVM cores requires the simulation to be setup slightly
differently.

Prior to this commit checking whether a core was a KVM core was only
possible via the CPUType which we may not always have.

Change-Id: Ibf6155ad631d5d5e93189d7376f022ea1baa685e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62351
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

src/python/gem5/components/processors/abstract_core.py

@@ -42,6 +42,15 @@ class AbstractCore(SubSystem):
     def get_isa(self) -> ISA:
         raise NotImplementedError
 
+    @abstractmethod
+    def is_kvm_core(self) -> bool:
+        """
+        KVM cores need setup differently than other cores. Frequently it's
+        useful to know whether a core is a KVM core or not. This function helps
+        with this.
+        """
+        raise NotImplementedError
+
     @abstractmethod
     def connect_icache(self, port: Port) -> None:
         """

src/python/gem5/components/processors/abstract_generator_core.py

@@ -54,6 +54,10 @@ class AbstractGeneratorCore(AbstractCore):
         super().__init__()
         self.port_end = PortTerminator()
 
+    @overrides(AbstractCore)
+    def is_kvm_core(self) -> bool:
+        return False
+
     @overrides(AbstractCore)
     def get_isa(self) -> ISA:
         return ISA.NULL

src/python/gem5/components/processors/base_cpu_core.py

@@ -60,6 +60,18 @@ class BaseCPUCore(AbstractCore):
         return self.core
 
     @overrides(AbstractCore)
+    def is_kvm_core(self) -> bool:
+
+        try:
+            from m5.objects import BaseKvmCPU
+
+            return isinstance(self.core, BaseKvmCPU)
+        except ImportError:
+            # If importing BaseKvmCPU throws an exception then it's because
+            # it's not compiled into the binary. If this is the case then this
+            # can't be a KVM core.
+            return False
+
     def get_isa(self) -> ISA:
         return self._isa
 

src/python/gem5/components/processors/switchable_processor.py

@@ -68,12 +68,10 @@ class SwitchableProcessor(AbstractProcessor):
                 core.set_switched_out(core not in self._current_cores)
                 all_cores.append(core)
 
-        self._prepare_kvm = CPUTypes.KVM in [
+        self._prepare_kvm = any(core.is_kvm_core() for core in all_cores)
-            core.get_type() for core in all_cores
-        ]
 
         if self._prepare_kvm:
-            if all_cores[0].get_type() != CPUTypes.KVM:
+            if not all_cores[0].is_kvm_core():
                 raise Exception(
                     "When using KVM, the switchable processor must start "
                     "with the KVM cores."
@@ -98,9 +96,7 @@ class SwitchableProcessor(AbstractProcessor):
 
             # To get the KVM CPUs to run on different host CPUs
             # Specify a different event queue for each CPU
-            kvm_cores = [
+            kvm_cores = [core for core in self.cores if core.is_kvm_core()]
-                core for core in self.cores if core.get_type() == CPUTypes.KVM
-            ]
             for i, core in enumerate(kvm_cores):
                 for obj in core.get_simobject().descendants():
                     obj.eventq_index = 0

src/python/gem5/simulate/simulator.py

@@ -283,10 +283,10 @@ class Simulator:
             # (for example, in `get_stats()`).
             self._root = root
 
-            if CPUTypes.KVM in [
+            if any(
-                core.get_type()
+                core.is_kvm_core()
                 for core in self._board.get_processor().get_cores()
-            ]:
+            ):
                 m5.ticks.fixGlobalFrequency()
                 root.sim_quantum = m5.ticks.fromSeconds(0.001)