Constant DEFAULT_KERNEL_CMDLINE 

pub const DEFAULT_KERNEL_CMDLINE: &str = "reboot=k panic=1 nomodule 8250.nr_uarts=0 i8042.noaux \
                                          i8042.nomux i8042.dumbkbd swiotlb=noforce";

Default guest kernel command line:

• reboot=k shut down the guest on reboot, instead of well… rebooting;
• panic=1 on panic, reboot after 1 second;
• nomodule disable loadable kernel module support;
• 8250.nr_uarts=0 disable 8250 serial interface;
• i8042.noaux do not probe the i8042 controller for an attached mouse (save boot time);
• i8042.nomux do not probe i8042 for a multiplexing controller (save boot time);
• i8042.dumbkbd do not attempt to control kbd state via the i8042 (save boot time).
• swiotlb=noforce disable software bounce buffers (SWIOTLB)