arm64: Unmask asynchronous aborts when in kernel mode

The asynchronous aborts are generally fatal for the kernel but they can
be masked via the pstate A bit. If a system error happens while in
kernel mode, it won't be visible until returning to user space. This
patch enables this kind of abort early to help identifying the cause.
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/irqflags.h

@@ -56,6 +56,9 @@ static inline void arch_local_irq_disable(void)
 #define local_fiq_enable()	asm("msr	daifclr, #1" : : : "memory")
 #define local_fiq_disable()	asm("msr	daifset, #1" : : : "memory")
 
+#define local_async_enable()	asm("msr	daifclr, #4" : : : "memory")
+#define local_async_disable()	asm("msr	daifset, #4" : : : "memory")
+
 /*
  * Save the current interrupt enable state.
  */

arch/arm64/kernel/setup.c

@@ -205,6 +205,11 @@ u64 __cpu_logical_map[NR_CPUS] = { [0 ... NR_CPUS-1] = INVALID_HWID };
 
 void __init setup_arch(char **cmdline_p)
 {
+	/*
+	 * Unmask asynchronous aborts early to catch possible system errors.
+	 */
+	local_async_enable();
+
 	setup_processor();
 
 	setup_machine_fdt(__fdt_pointer);

arch/arm64/kernel/smp.c

@@ -160,6 +160,7 @@ asmlinkage void secondary_start_kernel(void)
 
 	local_irq_enable();
 	local_fiq_enable();
+	local_async_enable();
 
 	/*
 	 * OK, it's off to the idle thread for us