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Adding support for ARM64 LCOW #2606

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ae98597
Adding support for ARM64 LCOW
Feb 20, 2026
757c31f
Address Review Comments
Mar 2, 2026
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9 changes: 9 additions & 0 deletions internal/uvm/create.go
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Original file line number Diff line number Diff line change
Expand Up @@ -189,6 +189,15 @@ func verifyOptions(_ context.Context, options interface{}) error {
return errors.New("resource partition ID and CPU group ID cannot be set at the same time")
}
}
if runtime.GOARCH == "arm64" {
// ARM64 specific checks for currently unsupported features. These can be removed when the features are supported on ARM64.
if opts.VPMemDeviceCount > 0 {
return errors.New("VPMem devices are not supported on ARM64")
}
if opts.KernelDirect {
return errors.New("KernelDirectBoot is not supported on ARM64")
}
}
case *OptionsWCOW:
if opts.EnableDeferredCommit && !opts.AllowOvercommit {
return errors.New("EnableDeferredCommit is not supported on physically backed VMs")
Expand Down
19 changes: 15 additions & 4 deletions internal/uvm/create_lcow.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@ import (
"net"
"os"
"path/filepath"
"runtime"
"strings"

"github.com/Microsoft/go-winio"
Expand Down Expand Up @@ -152,6 +153,11 @@ func defaultLCOWOSBootFilesPath() string {
func NewDefaultOptionsLCOW(id, owner string) *OptionsLCOW {
// Use KernelDirect boot by default on all builds that support it.
kernelDirectSupported := osversion.Build() >= 18286
var vPmemCount uint32 = DefaultVPMEMCount
if runtime.GOARCH == "arm64" {
kernelDirectSupported = false
vPmemCount = 0
}
opts := &OptionsLCOW{
Options: newDefaultOptions(id, owner),
KernelFile: KernelFile,
Expand All @@ -163,7 +169,7 @@ func NewDefaultOptionsLCOW(id, owner string) *OptionsLCOW {
ForwardStdout: false,
ForwardStderr: true,
OutputHandlerCreator: parseLogrus,
VPMemDeviceCount: DefaultVPMEMCount,
VPMemDeviceCount: vPmemCount,
VPMemSizeBytes: DefaultVPMemSizeBytes,
VPMemNoMultiMapping: osversion.Get().Build < osversion.V19H1,
PreferredRootFSType: PreferredRootFSTypeInitRd,
Expand All @@ -180,7 +186,6 @@ func NewDefaultOptionsLCOW(id, owner string) *OptionsLCOW {
}

opts.UpdateBootFilesPath(context.TODO(), defaultLCOWOSBootFilesPath())

return opts
}

Expand Down Expand Up @@ -807,14 +812,20 @@ func makeLCOWDoc(ctx context.Context, opts *OptionsLCOW, uvm *UtilityVM) (_ *hcs
vmDebugging := false
if opts.ConsolePipe != "" {
vmDebugging = true
kernelArgs += " 8250_core.nr_uarts=1 8250_core.skip_txen_test=1 console=ttyS0,115200"
if runtime.GOARCH == "arm64" {
kernelArgs += " console=ttyAMA0,115200"
} else {
kernelArgs += " 8250_core.nr_uarts=1 8250_core.skip_txen_test=1 console=ttyS0,115200"
}
doc.VirtualMachine.Devices.ComPorts = map[string]hcsschema.ComPort{
"0": { // Which is actually COM1
NamedPipe: opts.ConsolePipe,
},
}
} else {
kernelArgs += " 8250_core.nr_uarts=0"
if runtime.GOARCH != "arm64" {
kernelArgs += " 8250_core.nr_uarts=0"
}
}

if opts.EnableGraphicsConsole {
Expand Down