govmm: Define the number of supported vCPUs per architecture

Based on qhe QEMU supports on those architectures.

Signed-off-by: Samuel Ortiz <s.ortiz@apple.com>

src/runtime/pkg/govmm/vmm_amd64.go

@@ -0,0 +1,12 @@
+//
+// Copyright (c) 2018 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package govmm
+
+// MaxVCPUs returns the maximum number of vCPUs supported
+func MaxVCPUs() uint32 {
+	return uint32(240)
+}

src/runtime/pkg/govmm/vmm_arm64.go

@@ -0,0 +1,25 @@
+//
+// Copyright (c) 2018 Intel Corporation
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package govmm
+
+//In qemu, maximum number of vCPUs depends on the GIC version, or on how
+//many redistributors we can fit into the memory map.
+//related codes are under github.com/qemu/qemu/hw/arm/virt.c(Line 135 and 1306 in stable-2.11)
+//for now, qemu only supports v2 and v3, we treat v4 as v3 based on
+//backward compatibility.
+var gicList = map[uint32]uint32{
+	uint32(2): uint32(8),
+	uint32(3): uint32(123),
+	uint32(4): uint32(123),
+}
+
+var defaultGICVersion = uint32(3)
+
+// MaxVCPUs returns the maximum number of vCPUs supported
+func MaxVCPUs() uint32 {
+	return gicList[defaultGICVersion]
+}

src/runtime/pkg/govmm/vmm_ppc64le.go

@@ -0,0 +1,12 @@
+//
+// Copyright (c) 2018 IBM
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package qemu
+
+// MaxVCPUs returns the maximum number of vCPUs supported
+func MaxVCPUs() uint32 {
+	return uint32(128)
+}

src/runtime/pkg/govmm/vmm_s390x.go

@@ -0,0 +1,15 @@
+//
+// Copyright (c) 2018 IBM
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+
+package govmm
+
+// MaxVCPUs returns the maximum number of vCPUs supported
+func MaxVCPUs() uint32 {
+	// Max number of virtual Cpu defined in qemu. See
+ 	// https://github.com/qemu/qemu/blob/80422b00196a7af4c6efb628fae0ad8b644e98af/target/s390x/cpu.h#L55
+ 	// #define S390_MAX_CPUS 248
+ 	return uint32(248)
+}