arm64: log CPU boot modes

We currently don't log the boot mode for arm64 as we do for arm, and
without KVM the user is provided with no indication as to which mode(s)
CPUs were booted in, which can seriously hinder debugging in some cases.

Add logging to the boot path once all CPUs are up. Where CPUs are
mismatched in violation of the boot protocol, WARN and set a taint (as
we do for CPU other CPU feature mismatches) given that the
firmware/bootloader is buggy and should be fixed.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/setup.c

@@ -62,6 +62,7 @@
 #include <asm/memblock.h>
 #include <asm/psci.h>
 #include <asm/efi.h>
+#include <asm/virt.h>
 
 unsigned int processor_id;
 EXPORT_SYMBOL(processor_id);
@@ -207,8 +208,20 @@ static void __init smp_build_mpidr_hash(void)
 }
 #endif
 
+static void __init hyp_mode_check(void)
+{
+	if (is_hyp_mode_available())
+		pr_info("CPU: All CPU(s) started at EL2\n");
+	else if (is_hyp_mode_mismatched())
+		WARN_TAINT(1, TAINT_CPU_OUT_OF_SPEC,
+			   "CPU: CPUs started in inconsistent modes");
+	else
+		pr_info("CPU: All CPU(s) started at EL1\n");
+}
+
 void __init do_post_cpus_up_work(void)
 {
+	hyp_mode_check();
 	apply_alternatives_all();
 }