arm64: kpti: Use early_param for kpti= command-line option

commit b5b7dd64 upstream.

We inspect __kpti_forced early on as part of the cpufeature enable
callback which remaps the swapper page table using non-global entries.

Ensure that __kpti_forced has been updated to reflect the kpti=
command-line option before we start using it.

Fixes: ea1e3de8 ("arm64: entry: Add fake CPU feature for unmapping the kernel at EL0")
Cc: <stable@vger.kernel.org> # 4.16.x-
Reported-by: Wei Xu <xuwei5@hisilicon.com>
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Tested-by: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/kernel/cpufeature.c

@@ -877,7 +877,7 @@ static int __init parse_kpti(char *str)
 	__kpti_forced = enabled ? 1 : -1;
 	return 0;
 }
-__setup("kpti=", parse_kpti);
+early_param("kpti", parse_kpti);
 #endif	/* CONFIG_UNMAP_KERNEL_AT_EL0 */
 
 static const struct arm64_cpu_capabilities arm64_features[] = {