powerpc/64s/radix: Remove bolted-SLB address limit for per-cpu stacks

Radix MMU does not take SLB or TLB interrupts when accessing kernel
linear address. Remove this restriction for radix mode.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/setup_64.c

@@ -564,6 +564,9 @@ static __init u64 safe_stack_limit(void)
 	/* Other BookE, we assume the first GB is bolted */
 	return 1ul << 30;
 #else
+	if (early_radix_enabled())
+		return ULONG_MAX;
+
 	/* BookS, the first segment is bolted */
 	if (mmu_has_feature(MMU_FTR_1T_SEGMENT))
 		return 1UL << SID_SHIFT_1T;
@@ -578,7 +581,8 @@ void __init irqstack_early_init(void)
 
 	/*
 	 * Interrupt stacks must be in the first segment since we
-	 * cannot afford to take SLB misses on them.
+	 * cannot afford to take SLB misses on them. They are not
+	 * accessed in realmode.
 	 */
 	for_each_possible_cpu(i) {
 		softirq_ctx[i] = (struct thread_info *)
@@ -649,8 +653,9 @@ void __init emergency_stack_init(void)
 	 * aligned.
 	 *
 	 * Since we use these as temporary stacks during secondary CPU
-	 * bringup, we need to get at them in real mode. This means they
-	 * must also be within the RMO region.
+	 * bringup, machine check, system reset, and HMI, we need to get
+	 * at them in real mode. This means they must also be within the RMO
+	 * region.
 	 *
 	 * The IRQ stacks allocated elsewhere in this file are zeroed and
 	 * initialized in kernel/irq.c. These are initialized here in order