qemu: allow using legacy serial device for the console

This allows to get guest early boot logs which are usually
missed when virtconsole is used.
- It utilizes previous work on the govmm side:
https://github.com/kata-containers/govmm/pull/203
- unit test added

Fixes: #4237
Signed-off-by: Snir Sheriber <ssheribe@redhat.com>

src/runtime/config/configuration-qemu.toml.in

@@ -389,6 +389,9 @@ valid_entropy_sources = @DEFVALIDENTROPYSOURCES@
 # be default_memory.
 #enable_guest_swap = true
 
+# use legacy serial for guest console if available and implemented for architecture. Default false
+#use_legacy_serial = true
+
 [factory]
 # VM templating support. Once enabled, new VMs are created from template
 # using vm cloning. They will share the same initial kernel, initramfs and

src/runtime/pkg/katautils/config-settings.go.in

@@ -89,6 +89,7 @@ const defaultGuestSwap = false
 const defaultRootlessHypervisor = false
 const defaultDisableSeccomp = false
 const defaultVfioMode = "guest-kernel"
+const defaultLegacySerial = false
 
 var defaultSGXEPCSize = int64(0)
 

src/runtime/pkg/katautils/config.go

@@ -146,6 +146,7 @@ type hypervisor struct {
 	Rootless                       bool     `toml:"rootless"`
 	DisableSeccomp                 bool     `toml:"disable_seccomp"`
 	DisableSeLinux                 bool     `toml:"disable_selinux"`
+	LegacySerial                   bool     `toml:"use_legacy_serial"`
 }
 
 type runtime struct {
@@ -775,6 +776,7 @@ func newQemuHypervisorConfig(h hypervisor) (vc.HypervisorConfig, error) {
 		ConfidentialGuest:       h.ConfidentialGuest,
 		GuestSwap:               h.GuestSwap,
 		Rootless:                h.Rootless,
+		LegacySerial:            h.LegacySerial,
 	}, nil
 }
 
@@ -1132,6 +1134,7 @@ func GetDefaultHypervisorConfig() vc.HypervisorConfig {
 		GuestSwap:               defaultGuestSwap,
 		Rootless:                defaultRootlessHypervisor,
 		DisableSeccomp:          defaultDisableSeccomp,
+		LegacySerial:            defaultLegacySerial,
 	}
 }
 

src/runtime/virtcontainers/hypervisor.go

@@ -537,6 +537,9 @@ type HypervisorConfig struct {
 
 	// Disable selinux from the hypervisor process
 	DisableSeLinux bool
+
+	// Use legacy serial for the guest console
+	LegacySerial bool
 }
 
 // vcpu mapping from vcpu number to thread number

src/runtime/virtcontainers/qemu_amd64.go

@@ -122,6 +122,7 @@ func newQemuArch(config HypervisorConfig) (qemuArch, error) {
 			disableNvdimm:        config.DisableImageNvdimm,
 			dax:                  true,
 			protection:           noneProtection,
+			legacySerial:         config.LegacySerial,
 		},
 		vmFactory: factory,
 	}

src/runtime/virtcontainers/qemu_arch_base.go

@@ -169,6 +169,7 @@ type qemuArchBase struct {
 	vhost         bool
 	disableNvdimm bool
 	dax           bool
+	legacySerial  bool
 }
 
 const (
@@ -318,29 +319,49 @@ func (q *qemuArchBase) memoryTopology(memoryMb, hostMemoryMb uint64, slots uint8
 }
 
 func (q *qemuArchBase) appendConsole(_ context.Context, devices []govmmQemu.Device, path string) ([]govmmQemu.Device, error) {
-	serial := govmmQemu.SerialDevice{
-		Driver:        govmmQemu.VirtioSerial,
-		ID:            "serial0",
-		DisableModern: q.nestedRun,
-		MaxPorts:      uint(2),
+	var serial, console govmmQemu.Device
+	var consoleKernelParams []Param
+
+	if q.legacySerial {
+		serial = govmmQemu.LegacySerialDevice{
+			Chardev: "charconsole0",
+		}
+
+		console = govmmQemu.CharDevice{
+			Driver:   govmmQemu.LegacySerial,
+			Backend:  govmmQemu.Socket,
+			DeviceID: "console0",
+			ID:       "charconsole0",
+			Path:     path,
+		}
+
+		consoleKernelParams = []Param{
+			{"console", "ttyS0"},
+		}
+	} else {
+		serial = govmmQemu.SerialDevice{
+			Driver:        govmmQemu.VirtioSerial,
+			ID:            "serial0",
+			DisableModern: q.nestedRun,
+			MaxPorts:      uint(2),
+		}
+
+		console = govmmQemu.CharDevice{
+			Driver:   govmmQemu.Console,
+			Backend:  govmmQemu.Socket,
+			DeviceID: "console0",
+			ID:       "charconsole0",
+			Path:     path,
+		}
+
+		consoleKernelParams = []Param{
+			{"console", "hvc0"},
+			{"console", "hvc1"},
+		}
 	}
 
 	devices = append(devices, serial)
-
-	console := govmmQemu.CharDevice{
-		Driver:   govmmQemu.Console,
-		Backend:  govmmQemu.Socket,
-		DeviceID: "console0",
-		ID:       "charconsole0",
-		Path:     path,
-	}
-
 	devices = append(devices, console)
-
-	consoleKernelParams := []Param{
-		{"console", "hvc0"},
-		{"console", "hvc1"},
-	}
 	q.kernelParams = append(q.kernelParams, consoleKernelParams...)
 
 	return devices, nil

src/runtime/virtcontainers/qemu_arch_base_test.go

@@ -263,6 +263,34 @@ func TestQemuArchBaseAppendConsoles(t *testing.T) {
 	assert.Contains(qemuArchBase.kernelParams, Param{"console", "hvc1"})
 }
 
+func TestQemuArchBaseAppendConsolesLegacy(t *testing.T) {
+	var devices []govmmQemu.Device
+	var err error
+	assert := assert.New(t)
+	qemuArchBase := newQemuArchBase()
+	qemuArchBase.legacySerial = true
+
+	path := filepath.Join(filepath.Join(fs.MockRunStoragePath(), "test"), consoleSocket)
+
+	expectedOut := []govmmQemu.Device{
+		govmmQemu.LegacySerialDevice{
+			Chardev: "charconsole0",
+		},
+		govmmQemu.CharDevice{
+			Driver:   govmmQemu.LegacySerial,
+			Backend:  govmmQemu.Socket,
+			DeviceID: "console0",
+			ID:       "charconsole0",
+			Path:     path,
+		},
+	}
+
+	devices, err = qemuArchBase.appendConsole(context.Background(), devices, path)
+	assert.NoError(err)
+	assert.Equal(expectedOut, devices)
+	assert.Contains(qemuArchBase.kernelParams, Param{"console", "ttyS0"})
+}
+
 func TestQemuArchBaseAppendImage(t *testing.T) {
 	var devices []govmmQemu.Device
 	assert := assert.New(t)

src/runtime/virtcontainers/qemu_arm64.go

@@ -62,6 +62,7 @@ func newQemuArch(config HypervisorConfig) (qemuArch, error) {
 			disableNvdimm:        config.DisableImageNvdimm,
 			dax:                  true,
 			protection:           noneProtection,
+			legacySerial:         config.LegacySerial,
 		},
 	}
 

src/runtime/virtcontainers/qemu_ppc64le.go

@@ -74,6 +74,7 @@ func newQemuArch(config HypervisorConfig) (qemuArch, error) {
 			kernelParamsDebug:    kernelParamsDebug,
 			kernelParams:         kernelParams,
 			protection:           noneProtection,
+			legacySerial:         config.LegacySerial,
 		},
 	}
 

src/runtime/virtcontainers/qemu_s390x.go

@@ -66,6 +66,7 @@ func newQemuArch(config HypervisorConfig) (qemuArch, error) {
 			kernelParamsNonDebug: kernelParamsNonDebug,
 			kernelParamsDebug:    kernelParamsDebug,
 			kernelParams:         kernelParams,
+			legacySerial:         false,
 		},
 	}
 	// Set first bridge type to CCW