Nested virtualization with Linux VM

Sources/tart/Commands/Set.swift

@@ -17,6 +17,9 @@ struct Set: AsyncParsableCommand {
   @Option(help: "VM display resolution in a format of <width>x<height>. For example, 1200x800")
   var display: VMDisplayConfig?
 
+  @Flag(help: ArgumentHelp("Enable nested virtualization for the VM if supported."))
+  var nestedVirtualization: Bool = false
+
   @Flag(help: ArgumentHelp("Generate a new random MAC address for the VM."))
   var randomMAC: Bool = false
 
@@ -74,6 +77,10 @@ struct Set: AsyncParsableCommand {
       }
     #endif
 
+    if nestedVirtualization {
+      try vmConfig.enableNestedVirtualisation()
+    }
+
     try vmConfig.save(toURL: vmDir.configURL)
 
     if let disk = disk {

Sources/tart/Platform/Darwin.swift

@@ -58,7 +58,7 @@ struct UnsupportedHostOSError: Error, CustomStringConvertible {
       VZMacOSBootLoader()
     }
 
-    func platform(nvramURL: URL) throws -> VZPlatformConfiguration {
+    func platform(nvramURL: URL, enableNestedVirtualization: Bool) throws -> VZPlatformConfiguration {
       let result = VZMacPlatformConfiguration()
 
       result.machineIdentifier = ecid

Sources/tart/Platform/Linux.swift

@@ -2,6 +2,7 @@ import Virtualization
 
 @available(macOS 13, *)
 struct Linux: Platform {
+
   func os() -> OS {
     .linux
   }
@@ -14,8 +15,16 @@ struct Linux: Platform {
     return result
   }
 
-  func platform(nvramURL: URL) throws -> VZPlatformConfiguration {
-    VZGenericPlatformConfiguration()
+  func platform(nvramURL: URL, enableNestedVirtualization: Bool) throws -> VZPlatformConfiguration {
+    let result: VZGenericPlatformConfiguration = VZGenericPlatformConfiguration()
+
+    if #available(macOS 15.0, *) {
+      if VZGenericPlatformConfiguration.isNestedVirtualizationSupported {
+        result.isNestedVirtualizationEnabled = enableNestedVirtualization
+      }
+    }
+
+    return result
   }
 
   func graphicsDevice(vmConfig: VMConfig) -> VZGraphicsDeviceConfiguration {

Sources/tart/Platform/Platform.swift

@@ -3,7 +3,7 @@ import Virtualization
 protocol Platform: Codable {
   func os() -> OS
   func bootLoader(nvramURL: URL) throws -> VZBootLoader
-  func platform(nvramURL: URL) throws -> VZPlatformConfiguration
+  func platform(nvramURL: URL, enableNestedVirtualization: Bool) throws -> VZPlatformConfiguration
   func graphicsDevice(vmConfig: VMConfig) -> VZGraphicsDeviceConfiguration
   func keyboards() -> [VZKeyboardConfiguration]
   func pointingDevices() -> [VZPointingDeviceConfiguration]

Sources/tart/VM.swift

@@ -142,6 +142,7 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
       vmDir: VMDirectory,
       ipswURL: URL,
       diskSizeGB: UInt16,
+      nestedVirtualization: Bool = false,
       network: Network = NetworkShared(),
       additionalStorageDevices: [VZStorageDeviceConfiguration] = [],
       directorySharingDevices: [VZDirectorySharingDeviceConfiguration] = [],
@@ -231,7 +232,7 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
     try vmDir.resizeDisk(diskSizeGB)
 
     // Create config
-    let config = VMConfig(platform: Linux(), cpuCountMin: 4, memorySizeMin: 4096 * 1024 * 1024)
+    let config = VMConfig(platform: Linux(), cpuCountMin: 1, memorySizeMin: 512 * 1024 * 1024)
     try config.save(toURL: vmDir.configURL)
 
     return try VM(vmDir: vmDir)
@@ -309,7 +310,7 @@ class VM: NSObject, VZVirtualMachineDelegate, ObservableObject {
     configuration.memorySize = vmConfig.memorySize
 
     // Platform
-    configuration.platform = try vmConfig.platform.platform(nvramURL: nvramURL)
+    configuration.platform = try vmConfig.platform.platform(nvramURL: nvramURL, enableNestedVirtualization: vmConfig.nestedVirtualization)
 
     // Display
     configuration.graphicsDevices = [vmConfig.platform.graphicsDevice(vmConfig: vmConfig)]

Sources/tart/VMConfig.swift

@@ -14,6 +14,20 @@ class LessThanMinimalResourcesError: NSObject, LocalizedError {
   }
 }
 
+class UnsupportedNestedVirtualizationError: NSObject, LocalizedError {
+  var userExplanation: String
+
+  init(_ userExplanation: String) {
+    self.userExplanation = userExplanation
+  }
+
+  override var description: String {
+    get {
+      "UnsupportedNestedVirtualizationError: \(userExplanation)"
+    }
+  }
+}
+
 enum CodingKeys: String, CodingKey {
   case version
   case os
@@ -24,6 +38,7 @@ enum CodingKeys: String, CodingKey {
   case memorySize
   case macAddress
   case display
+  case nestedVirtualization
 
   // macOS-specific keys
   case ecid
@@ -52,7 +67,8 @@ struct VMConfig: Codable {
   private(set) var memorySize: UInt64
   var macAddress: VZMACAddress
   var display: VMDisplayConfig = VMDisplayConfig()
-
+  private(set) var nestedVirtualization: Bool
+
   init(
     platform: Platform,
     cpuCountMin: Int,
@@ -65,31 +81,32 @@ struct VMConfig: Codable {
     self.macAddress = macAddress
     self.cpuCountMin = cpuCountMin
     self.memorySizeMin = memorySizeMin
+    nestedVirtualization = false
     cpuCount = cpuCountMin
     memorySize = memorySizeMin
   }
-
+  
   init(fromJSON: Data) throws {
     self = try Config.jsonDecoder().decode(Self.self, from: fromJSON)
   }
-
+  
   init(fromURL: URL) throws {
     self = try Self(fromJSON: try Data(contentsOf: fromURL))
   }
-
+  
   func toJSON() throws -> Data {
     try Config.jsonEncoder().encode(self)
   }
-
+  
   func save(toURL: URL) throws {
     let encoder = JSONEncoder()
     encoder.outputFormatting = .prettyPrinted
     try encoder.encode(self).write(to: toURL)
   }
-
+  
   init(from decoder: Decoder) throws {
     let container = try decoder.container(keyedBy: CodingKeys.self)
-
+    
     version = try container.decode(Int.self, forKey: .version)
     os = try container.decodeIfPresent(OS.self, forKey: .os) ?? .darwin
     arch = try container.decodeIfPresent(Architecture.self, forKey: .arch) ?? .arm64
@@ -110,7 +127,6 @@ struct VMConfig: Codable {
     cpuCount = try container.decode(Int.self, forKey: .cpuCount)
     memorySizeMin = try container.decode(UInt64.self, forKey: .memorySizeMin)
     memorySize = try container.decode(UInt64.self, forKey: .memorySize)
-
     let encodedMacAddress = try container.decode(String.self, forKey: .macAddress)
     guard let macAddress = VZMACAddress.init(string: encodedMacAddress) else {
       throw DecodingError.dataCorruptedError(
@@ -119,13 +135,14 @@ struct VMConfig: Codable {
         debugDescription: "failed to initialize VZMacAddress using the provided value")
     }
     self.macAddress = macAddress
-
+    
     display = try container.decodeIfPresent(VMDisplayConfig.self, forKey: .display) ?? VMDisplayConfig()
+    nestedVirtualization = try container.decodeIfPresent(Bool.self, forKey: .nestedVirtualization) ?? false
   }
-
+  
   func encode(to encoder: Encoder) throws {
     var container = encoder.container(keyedBy: CodingKeys.self)
-
+    
     try container.encode(version, forKey: .version)
     try container.encode(os, forKey: .os)
     try container.encode(arch, forKey: .arch)
@@ -136,33 +153,49 @@ struct VMConfig: Codable {
     try container.encode(memorySize, forKey: .memorySize)
     try container.encode(macAddress.string, forKey: .macAddress)
     try container.encode(display, forKey: .display)
+    try container.encode(nestedVirtualization, forKey: .nestedVirtualization)
   }
-
+  
   mutating func setCPU(cpuCount: Int) throws {
     if os == .darwin && cpuCount < cpuCountMin {
       throw LessThanMinimalResourcesError("VM should have \(cpuCountMin) CPU cores"
         + " at minimum (requested \(cpuCount))")
     }
-
+    
     if cpuCount < VZVirtualMachineConfiguration.minimumAllowedCPUCount {
       throw LessThanMinimalResourcesError("VM should have \(VZVirtualMachineConfiguration.minimumAllowedCPUCount) CPU cores"
         + " at minimum (requested \(cpuCount))")
     }
-
+    
     self.cpuCount = cpuCount
   }
-
+  
   mutating func setMemory(memorySize: UInt64) throws {
     if os == .darwin && memorySize < memorySizeMin {
       throw LessThanMinimalResourcesError("VM should have \(memorySizeMin) bytes"
         + " of memory at minimum (requested \(memorySize))")
     }
-
+    
     if memorySize < VZVirtualMachineConfiguration.minimumAllowedMemorySize {
       throw LessThanMinimalResourcesError("VM should have \(VZVirtualMachineConfiguration.minimumAllowedMemorySize) bytes"
         + " of memory at minimum (requested \(memorySize))")
     }
-
+    
     self.memorySize = memorySize
   }
+
+  mutating func enableNestedVirtualisation() throws {
+    if os == .darwin && nestedVirtualization {
+      throw UnsupportedNestedVirtualizationError("Nested virtualization is not supported for MacOS virtual machines")
+    }
+
+    if #available(macOS 15.0, *) {
+      if !VZGenericPlatformConfiguration.isNestedVirtualizationSupported {
+        throw UnsupportedNestedVirtualizationError("Nested virtualization is not supported on this hardware")
+      }
+      self.nestedVirtualization = true
+    } else {
+      throw UnsupportedNestedVirtualizationError("Nested virtualization requires macOS 15.0 or later")
+    }
+  }
 }