Add virtualization support for containers (#377)

Author: dcantah

Package.resolved

@@ -47,6 +47,8 @@ public struct ContainerConfiguration: Sendable, Codable {
     public var resources: Resources = .init()
     /// Name of the runtime that supports the container
     public var runtimeHandler: String = "container-runtime-linux"
+    /// Configure exposing virtualization support in the container.
+    public var virtualization: Bool = false
 
     enum CodingKeys: String, CodingKey {
         case id
@@ -64,6 +66,7 @@ public struct ContainerConfiguration: Sendable, Codable {
         case platform
         case resources
         case runtimeHandler
+        case virtualization
     }
 
     /// Create a configuration from the supplied Decoder, initializing missing
@@ -86,6 +89,7 @@ public struct ContainerConfiguration: Sendable, Codable {
         platform = try container.decodeIfPresent(ContainerizationOCI.Platform.self, forKey: .platform) ?? .current
         resources = try container.decodeIfPresent(Resources.self, forKey: .resources) ?? .init()
         runtimeHandler = try container.decodeIfPresent(String.self, forKey: .runtimeHandler) ?? "container-runtime-linux"
+        virtualization = try container.decodeIfPresent(Bool.self, forKey: .virtualization) ?? false
     }
 
     public struct DNSConfiguration: Sendable, Codable {

Sources/ContainerClient/Core/ContainerConfiguration.swift

@@ -148,6 +148,13 @@ public struct Flags {
 
         @Option(name: [.customLong("label"), .short], help: "Add a key=value label to the container")
         public var labels: [String] = []
+
+        @Flag(
+            name: [.customLong("virtualization")],
+            help:
+                "Expose virtualization capabilities to the container. (Host must have nested virtualization support, and guest kernel must have virtualization capabilities enabled)"
+        )
+        public var virtualization: Bool = false
     }
 
     public struct Progress: ParsableArguments {

Sources/ContainerClient/Flags.swift

@@ -150,6 +150,8 @@ public struct Utility {
         mounts.append(contentsOf: volumes)
         config.mounts = mounts
 
+        config.virtualization = management.virtualization
+
         if management.networks.isEmpty {
             config.networks = [ClientNetwork.defaultNetworkName]
         } else {

Sources/ContainerClient/Utility.swift

@@ -696,6 +696,8 @@ public actor SandboxService {
         czConfig.sysctl = config.sysctls.reduce(into: [String: String]()) {
             $0[$1.key] = $1.value
         }
+        // If the host doesn't support this, we'll throw on container creation.
+        czConfig.virtualization = config.virtualization
 
         for mount in config.mounts {
             if try mount.isSocket() {

Sources/Services/ContainerSandboxService/SandboxService.swift

@@ -286,6 +286,32 @@ Use the `--boot` option to see the logs for the virtual machine boot and init pr
 %
 </pre>
 
+## Expose virtualization capabilities to a container
+
+> [!NOTE]
+> This feature requires a M3 or newer Apple silicon machine and a Linux kernel that supports virtualization. For a kernel configuration that has all of the right features enabled, see https://github.com/apple/containerization/blob/0.5.0/kernel/config-arm64#L602.
+
+You can enable virtualization capabilities in containers by using the `--virtualization` option of `container run` and `container create`.
+
+If your machine does not have support for nested virtualization, you will see the following:
+
+```console
+container run --name nested-virtualization --virtualization --kernel /path/to/a/kernel/with/virtualization/support --rm ubuntu:latest sh -c "dmesg | grep kvm"
+Error: unsupported: "nested virtualization is not supported on the platform"
+```
+
+When nested virtualization is enabled successfully, `dmesg` will show output like the following:
+
+```console
+container run --name nested-virtualization --virtualization --kernel /path/to/a/kernel/with/virtualization/support --rm ubuntu:latest sh -c "dmesg | grep kvm"
+[    0.017245] kvm [1]: IPA Size Limit: 40 bits
+[    0.017499] kvm [1]: GICv3: no GICV resource entry
+[    0.017501] kvm [1]: disabling GICv2 emulation
+[    0.017506] kvm [1]: GIC system register CPU interface enabled
+[    0.017685] kvm [1]: vgic interrupt IRQ9
+[    0.017893] kvm [1]: Hyp mode initialized successfully
+```
+
 ## Configure container defaults
 
 `container` uses macOS user defaults to store configuration settings that persist between sessions. You can customize various aspects of container behavior, including build settings, default images, and network configuration.