qemu: use -cpu host by default

`-cpu host` seemed to cause kernel panic with QEMU 5.2 on Intel Mac,
but seems to work well with QEMU 6.1 now.

The behavior can be rolled back by specifying an env var like
`QEMU_SYSTEM_X86_64=qemu-system-x86_64 -cpu Haswell-v4` or
`QEMU_SYSTEM_AARCH64=qemu-system-aarch64 -cpu cortex-a72` .

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

README.md

@@ -149,8 +149,7 @@ See [`./pkg/limayaml/default.yaml`](./pkg/limayaml/default.yaml).
 
 The current default spec:
 - OS: Ubuntu 21.04 (Hirsute Hippo)
-- CPU (x86\_64): Haswell v4, 4 cores
-- CPU (aarch64): Cortex A72, 4 cores
+- CPU: 4 cores
 - Memory: 4 GiB
 - Disk: 100 GiB
 - Mounts: `~` (read-only), `/tmp/lima` (writable)

pkg/qemu/qemu.go

@@ -198,12 +198,18 @@ func Cmdline(cfg Config) (string, []string, error) {
 	}
 	switch y.Arch {
 	case limayaml.X8664:
-		// NOTE: "-cpu host" seems to cause kernel panic
-		// (MacBookPro 2020, Intel(R) Core(TM) i7-1068NG7 CPU @ 2.30GHz, macOS 11.3, Ubuntu 21.04)
-		args = appendArgsIfNoConflict(args, "-cpu", "Haswell-v4")
+		cpu := "Haswell-v4"
+		if isNativeArch(y.Arch) {
+			cpu = "host"
+		}
+		args = appendArgsIfNoConflict(args, "-cpu", cpu)
 		args = appendArgsIfNoConflict(args, "-machine", "q35,accel="+accel)
 	case limayaml.AARCH64:
-		args = appendArgsIfNoConflict(args, "-cpu", "cortex-a72")
+		cpu := "cortex-a72"
+		if isNativeArch(y.Arch) {
+			cpu = "host"
+		}
+		args = appendArgsIfNoConflict(args, "-cpu", cpu)
 		args = appendArgsIfNoConflict(args, "-machine", "virt,accel="+accel+",highmem=off")
 	}
 
@@ -355,11 +361,14 @@ func getExe(arch limayaml.Arch) (string, []string, error) {
 	return exe, args, nil
 }
 
-func getAccel(arch limayaml.Arch) string {
+func isNativeArch(arch limayaml.Arch) bool {
 	nativeX8664 := arch == limayaml.X8664 && runtime.GOARCH == "amd64"
 	nativeAARCH64 := arch == limayaml.AARCH64 && runtime.GOARCH == "arm64"
-	native := nativeX8664 || nativeAARCH64
-	if native {
+	return nativeX8664 || nativeAARCH64
+}
+
+func getAccel(arch limayaml.Arch) string {
+	if isNativeArch(arch) {
 		switch runtime.GOOS {
 		case "darwin":
 			return "hvf"