qemu: avoid Property 'host-arm-cpu.sme' not found

.codespellrc

@@ -6,7 +6,7 @@
 skip = .git,go.mod,go.sum,*.pb.desc,*/node_modules/*,*/public/js/*,*/public/scss/*
 
 # Comma separated list of words to be ignored. Words must be lowercased.
-ignore-words-list = ans,distroname,testof,hda,ststr,archtypes
+ignore-words-list = ans,distroname,testof,hda,ststr,archtypes,sme
 
 # Check file names as well.
 check-filenames = true

pkg/limayaml/defaults.go

@@ -14,6 +14,7 @@ import (
 	"slices"
 	"strconv"
 	"strings"
+	"sync"
 	"text/template"
 
 	"github.com/coreos/go-semver/semver"
@@ -1173,9 +1174,44 @@ func IsAccelOS() bool {
 	return false
 }
 
+var (
+	hasSMEDarwin     bool
+	hasSMEDarwinOnce sync.Once
+)
+
+func init() {
+	hasSMEDarwinOnce.Do(func() {
+		hasSMEDarwin = hasSMEDarwinFn()
+	})
+}
+
+func hasSMEDarwinFn() bool {
+	if runtime.GOOS != "darwin" || runtime.GOARCH != "arm64" {
+		return false
+	}
+	// golang.org/x/sys/cpu does not support inspecting the availability of SME yet
+	s, err := osutil.Sysctl("hw.optional.arm.FEAT_SME")
+	if err != nil {
+		logrus.WithError(err).Debug("failed to check hw.optional.arm.FEAT_SME")
+	}
+	return s == "1"
+}
+
 func HasHostCPU() bool {
 	switch runtime.GOOS {
-	case "darwin", "linux":
+	case "darwin":
+		if hasSMEDarwin {
+			// SME is available since Apple M4 running macOS 15.2.
+			//
+			// However, QEMU is not ready to handle SME yet.
+			//
+			// https://github.com/lima-vm/lima/issues/3032
+			// https://gitlab.com/qemu-project/qemu/-/issues/2665
+			// https://gitlab.com/qemu-project/qemu/-/issues/2721
+			return false
+		}
+		return true
+	case "linux":
 		return true
 	case "netbsd", "windows":
 		return false
@@ -1185,8 +1221,8 @@ func HasHostCPU() bool {
 }
 
 func HasMaxCPU() bool {
-	// WHPX: Unexpected VP exit code 4
-	return runtime.GOOS != "windows"
+	// windows: WHPX: Unexpected VP exit code 4
+	return HasHostCPU()
 }
 
 func IsNativeArch(arch Arch) bool {

pkg/osutil/osutil_unix.go

@@ -3,7 +3,11 @@
 package osutil
 
 import (
+	"bytes"
+	"fmt"
 	"os"
+	"os/exec"
+	"strings"
 	"syscall"
 
 	"golang.org/x/sys/unix"
@@ -16,3 +20,15 @@ func Dup2(oldfd, newfd int) (err error) {
 func SignalName(sig os.Signal) string {
 	return unix.SignalName(sig.(syscall.Signal))
 }
+
+func Sysctl(name string) (string, error) {
+	var stderrBuf bytes.Buffer
+	cmd := exec.Command("sysctl", "-n", name)
+	cmd.Stderr = &stderrBuf
+	stdout, err := cmd.Output()
+	if err != nil {
+		return "", fmt.Errorf("failed to run %v: %w (stdout=%q, stderr=%q)", cmd.Args, err,
+			string(stdout), stderrBuf.String())
+	}
+	return strings.TrimSuffix(string(stdout), "\n"), nil
+}

pkg/osutil/osutil_windows.go

@@ -1,6 +1,7 @@
 package osutil
 
 import (
+	"errors"
 	"fmt"
 	"io/fs"
 	"os"
@@ -48,3 +49,7 @@ func SignalName(sig os.Signal) string {
 		return fmt.Sprintf("Signal(%d)", sig)
 	}
 }
+
+func Sysctl(name string) (string, error) {
+	return "", errors.New("sysctl: unimplemented on Windows")
+}