In order to be able to disable Pointer Authentication at runtime, whether it is for testing purposes, or to work around HW issues, let's add support for overriding the ID_AA64ISAR1_EL1.{GPI,GPA,API,APA} fields. This is further mapped on the arm64.nopauth command-line alias. Signed-off-by: Marc Zyngier <maz@kernel.org> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: David Brazdil <dbrazdil@google.com> Tested-by: Srinivas Ramana <sramana@codeaurora.org> Link: https://lore.kernel.org/r/20210208095732.3267263-23-maz@kernel.org Signed-off-by: Will Deacon <will@kernel.org>