kvm: Passthrough host CPU in order to allow nesting

Before this patch the virtual CPU was the stock qemu CPU, in the sense that
the virtual CPU features were set according to the default qemu CPU.

With this change the CPU features of the host will be copied at start to the
domain definition. This includes features like svm and vmx, which in turn allow
to run nested virtualization if the host is configured accordingly i.e.
`kvm_intel nested=y` in `/etc/modprobe.d/kvm.conf`.

To turn on nesting, a user has to specify `--kvm-cpu-model host-model` when
creating the VM.

Resolves kubernetes#2553

Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>

cmd/minikube/cmd/start.go

@@ -61,6 +61,7 @@ const (
 	networkPlugin         = "network-plugin"
 	hypervVirtualSwitch   = "hyperv-virtual-switch"
 	kvmNetwork            = "kvm-network"
+	kvmCPUModel           = "kvm-cpu-model"
 	keepContext           = "keep-context"
 	createMount           = "mount"
 	featureGates          = "feature-gates"
@@ -145,6 +146,7 @@ func runStart(cmd *cobra.Command, args []string) {
 		HostOnlyCIDR:        viper.GetString(hostOnlyCIDR),
 		HypervVirtualSwitch: viper.GetString(hypervVirtualSwitch),
 		KvmNetwork:          viper.GetString(kvmNetwork),
+		KvmCPUModel:         viper.GetString(kvmCPUModel),
 		Downloader:          pkgutil.DefaultDownloader{},
 		DisableDriverMounts: viper.GetBool(disableDriverMounts),
 		UUID:                viper.GetString(uuid),
@@ -379,6 +381,7 @@ func init() {
 	startCmd.Flags().String(hostOnlyCIDR, "192.168.99.1/24", "The CIDR to be used for the minikube VM (only supported with Virtualbox driver)")
 	startCmd.Flags().String(hypervVirtualSwitch, "", "The hyperv virtual switch name. Defaults to first found. (only supported with HyperV driver)")
 	startCmd.Flags().String(kvmNetwork, "default", "The KVM network name. (only supported with KVM driver)")
+	startCmd.Flags().String(kvmCPUModel, "custom", "The KVM CPU model name. (only supported with KVM driver)")
 	startCmd.Flags().String(xhyveDiskDriver, "ahci-hd", "The disk driver to use [ahci-hd|virtio-blk] (only supported with xhyve driver)")
 	startCmd.Flags().StringSlice(NFSShare, []string{}, "Local folders to share with Guest via NFS mounts (Only supported on with hyperkit now)")
 	startCmd.Flags().String(NFSSharesRoot, "/nfsshares", "Where to root the NFS Shares (defaults to /nfsshares, only supported with hyperkit now)")

docs/drivers.md

@@ -54,6 +54,16 @@ To use the driver you would do:
 minikube start --vm-driver kvm2
 ```
 
+##### Nesting
+
+The KVM2 driver allows to run [nested VMs](https://en.wikipedia.org/wiki/Virtualization#Nested_virtualization)
+if the right CPU model is specyfied when launching minikube:
+
+```shell
+minikube --start --vm-driver kvm2 --kvm-cpu-model host-model
+```
+
+
 #### KVM driver
 
 Minikube is currently tested against [`docker-machine-driver-kvm` v0.10.0](https://github.com/dhiltgen/docker-machine-kvm/releases).

pkg/drivers/kvm/domain.go

@@ -37,6 +37,7 @@ const domainTmpl = `
     <apic/>
     <pae/>
   </features>
+  <cpu mode='{{.CPUModel}}'/>
   <os>
     <type>hvm</type>
     <boot dev='cdrom'/>

pkg/drivers/kvm/kvm.go

@@ -44,6 +44,9 @@ type Driver struct {
 	// How many cpus to allocate to the VM
 	CPU int
 
+	// What CPU model to expose
+	CPUModel string
+
 	// The name of the default network
 	Network string
 
@@ -83,6 +86,7 @@ func NewDriver(hostName, storePath string) *Driver {
 		CommonDriver:   &pkgdrivers.CommonDriver{},
 		Boot2DockerURL: constants.DefaultIsoUrl,
 		CPU:            constants.DefaultCPUS,
+		CPUModel:       constants.DefaultCPUModel,
 		DiskSize:       util.CalculateDiskSizeInMB(constants.DefaultDiskSize),
 		Memory:         constants.DefaultMemory,
 		PrivateNetwork: defaultPrivateNetworkName,

pkg/minikube/cluster/cluster_linux.go

@@ -33,6 +33,7 @@ type kvmDriver struct {
 	Memory         int
 	DiskSize       int
 	CPU            int
+	CPUModel       string
 	Network        string
 	PrivateNetwork string
 	ISO            string
@@ -71,6 +72,7 @@ func createKVM2Host(config MachineConfig) *kvmDriver {
 		},
 		Memory:         config.Memory,
 		CPU:            config.CPUs,
+		CPUModel:       config.KvmCPUModel,
 		Network:        config.KvmNetwork,
 		PrivateNetwork: "minikube-net",
 		Boot2DockerURL: config.Downloader.GetISOFileURI(config.MinikubeISO),

pkg/minikube/cluster/types.go

@@ -35,6 +35,7 @@ type MachineConfig struct {
 	HostOnlyCIDR        string // Only used by the virtualbox driver
 	HypervVirtualSwitch string
 	KvmNetwork          string             // Only used by the KVM driver
+	KvmCPUModel         string             // Only used by the KVM driver
 	Downloader          util.ISODownloader `json:"-"`
 	DockerOpt           []string           // Each entry is formatted as KEY=VALUE.
 	DisableDriverMounts bool               // Only used by virtualbox and xhyve

pkg/minikube/constants/constants.go

@@ -89,6 +89,7 @@ const (
 	ShaSuffix           = ".sha256"
 	DefaultMemory       = 2048
 	DefaultCPUS         = 2
+	DefaultCPUModel     = "custom"
 	DefaultDiskSize     = "20g"
 	MinimumDiskSizeMB   = 2000
 	DefaultVMDriver     = "virtualbox"