x86 kernel reboot parameters

reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] | p[ci]
warm   Don't set the cold reboot flag
cold   Set the cold reboot flag
bios   Reboot by jumping through the BIOS (only for X86_32)
smp    Reboot by executing reset on BSP or other CPU (only for X86_32)
triple Force a triple fault (init)
kbd    Use the keyboard controller. cold reset (default)
acpi   Use the RESET_REG in the FADT
efi    Use efi reset_system runtime service
pci    Use the so-called "PCI reset register", CF9
force  Avoid anything that could hang.