[ Upstream commit dda520d07b95072a0b63f6c52a8eb566d08ea897 ] QEMU has a -no-reboot option, which halts instead of reboots when the guest asks to reboot. This is invaluable when used with CONFIG_PANIC_TIMEOUT=-1 (and panic_on_warn), because it allows panics and warnings to be caught immediately in CI. Implement this in UML too, by way of a basic setup param. Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com> Signed-off-by: Richard Weinberger <richard@nod.at> Signed-off-by: Sasha Levin <sashal@kernel.org>