Merge pull request #1767 from nanjj/rtcbase

incusd/instance/qemu: rtc base localtime for windows

Author: stgraber

doc/.wordlist.txt

@@ -234,6 +234,7 @@ RESTful
 RHEL
 rootfs
 RSA
+RTC
 rST
 runtime
 SATA

doc/howto/instances_create.md

@@ -111,6 +111,16 @@ The list of supported clouds and instance types can be found at [`https://github
 
 ### Launch a VM that boots from an ISO
 
+```{note}
+When creating a Windows virtual machine, make sure to set the `image.os` property to something starting with `Windows`.
+Doing so will tell Incus to expect Windows to be running inside of the virtual machine and to tweak behavior accordingly.
+
+This notably will cause:
+ - Some unsupported virtual devices to be disabled
+ - The {abbr}`RTC (Real Time Clock)` clock to be based on system local time rather than UTC
+ - IOMMU handling to switch to an Intel IOMMU controller
+```
+
 To launch a VM that boots from an ISO, you must first create a VM.
 Let's assume that we want to create a VM and install it from the ISO image.
 In this scenario, use the following command to create an empty VM:

internal/server/instance/drivers/driver_qemu.go

@@ -1624,6 +1624,11 @@ func (d *qemu) start(stateful bool, op *operationlock.InstanceOperation) error {
 		}
 	}
 
+	// Set RTC to localtime on Windows.
+	if d.isWindows() {
+		qemuArgs = append(qemuArgs, "-rtc", "base=localtime")
+	}
+
 	// SMBIOS only on x86_64 and aarch64.
 	if d.architectureSupportsUEFI(d.architecture) {
 		qemuArgs = append(qemuArgs, "-smbios", "type=2,manufacturer=LinuxContainers,product=Incus")
@@ -3340,11 +3345,16 @@ func (d *qemu) deviceBootPriorities(base int) (map[string]int, error) {
 	return sortedDevs, nil
 }
 
+// isWindows returns whether the VM is Windows.
+func (d *qemu) isWindows() bool {
+	return strings.Contains(strings.ToLower(d.expandedConfig["image.os"]), "windows")
+}
+
 // generateQemuConfig generates the QEMU configuration.
 func (d *qemu) generateQemuConfig(cpuInfo *cpuTopology, mountInfo *storagePools.MountInfo, busName string, vsockFD int, devConfs []*deviceConfig.RunConfig, fdFiles *[]*os.File) ([]monitorHook, error) {
 	var monHooks []monitorHook
 
-	isWindows := strings.Contains(strings.ToLower(d.expandedConfig["image.os"]), "windows")
+	isWindows := d.isWindows()
 	conf := qemuBase(&qemuBaseOpts{d.Architecture(), util.IsTrue(d.expandedConfig["security.iommu"])})
 
 	err := d.addCPUMemoryConfig(&conf, cpuInfo)