diff --git a/README.md b/README.md
index fe21ba1df785bb..f42a15c258c5a8 100644
--- a/README.md
+++ b/README.md
@@ -5,4 +5,4 @@ Contains patches for:
 * virtio-iommu from https://jpbrucker.net/git/linux/log/?h=virtio-iommu/acpi (7616abe11cd1e0224bbd150626564db70bb07c31)
 * Support for virtio-watchdog
 * Bug fix: to support using ACPI reboot rather than EFI reboot
-
+* Log boot time via debug port `0x80` (details: https://github.com/cloud-hypervisor/cloud-hypervisor/blob/main/docs/debug-port.md)
diff --git a/init/main.c b/init/main.c
index bcd132d4e7bddf..54c4b7fbf80f25 100644
--- a/init/main.c
+++ b/init/main.c
@@ -935,6 +935,8 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 	char *command_line;
 	char *after_dashes;
 
+	outb(0x40, 0x80);
+
 	set_task_stack_end_magic(&init_task);
 	smp_setup_processor_id();
 	debug_objects_early_init();
@@ -1528,6 +1530,8 @@ static int __ref kernel_init(void *unused)
 
 	do_sysctl_args();
 
+	outb(0x41, 0x80);
+
 	if (ramdisk_execute_command) {
 		ret = run_init_process(ramdisk_execute_command);
 		if (!ret)