arm64: smp: Rework early feature mismatched detection

Rather than add additional variables to detect specific early feature
mismatches with secondary CPUs, we can instead dedicate the upper bits
of the CPU boot status word to flag specific mismatches.

This allows us to communicate both granule and VA-size mismatches back
to the primary CPU without the need for additional book-keeping.
Tested-by: Steve Capper <steve.capper@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/smp.h

@@ -17,15 +17,20 @@
 #define __ASM_SMP_H
 
 /* Values for secondary_data.status */
+#define CPU_STUCK_REASON_SHIFT		(8)
+#define CPU_BOOT_STATUS_MASK		((1U << CPU_STUCK_REASON_SHIFT) - 1)
 
-#define CPU_MMU_OFF		(-1)
-#define CPU_BOOT_SUCCESS	(0)
+#define CPU_MMU_OFF			(-1)
+#define CPU_BOOT_SUCCESS		(0)
 /* The cpu invoked ops->cpu_die, synchronise it with cpu_kill */
-#define CPU_KILL_ME		(1)
+#define CPU_KILL_ME			(1)
 /* The cpu couldn't die gracefully and is looping in the kernel */
-#define CPU_STUCK_IN_KERNEL	(2)
+#define CPU_STUCK_IN_KERNEL		(2)
 /* Fatal system error detected by secondary CPU, crash the system */
-#define CPU_PANIC_KERNEL	(3)
+#define CPU_PANIC_KERNEL		(3)
+
+#define CPU_STUCK_REASON_52_BIT_VA	(1U << CPU_STUCK_REASON_SHIFT)
+#define CPU_STUCK_REASON_NO_GRAN	(2U << CPU_STUCK_REASON_SHIFT)
 
 #ifndef __ASSEMBLY__
 

arch/arm64/kernel/head.S

@@ -809,13 +809,8 @@ ENTRY(__cpu_secondary_check52bitva)
 	and	x0, x0, #(0xf << ID_AA64MMFR2_LVA_SHIFT)
 	cbnz	x0, 2f
 
-	adr_l	x0, va52mismatch
-	mov	w1, #1
-	strb	w1, [x0]
-	dmb	sy
-	dc	ivac, x0	// Invalidate potentially stale cache line
-
-	update_early_cpu_boot_status CPU_STUCK_IN_KERNEL, x0, x1
+	update_early_cpu_boot_status \
+		CPU_STUCK_IN_KERNEL | CPU_STUCK_REASON_52_BIT_VA, x0, x1
 1:	wfe
 	wfi
 	b	1b
@@ -826,7 +821,8 @@ ENDPROC(__cpu_secondary_check52bitva)
 
 __no_granule_support:
 	/* Indicate that this CPU can't boot and is stuck in the kernel */
-	update_early_cpu_boot_status CPU_STUCK_IN_KERNEL, x1, x2
+	update_early_cpu_boot_status \
+		CPU_STUCK_IN_KERNEL | CPU_STUCK_REASON_NO_GRAN, x1, x2
 1:
 	wfe
 	wfi

arch/arm64/kernel/smp.c

@@ -108,7 +108,6 @@ static int boot_secondary(unsigned int cpu, struct task_struct *idle)
 }
 
 static DECLARE_COMPLETION(cpu_running);
-bool va52mismatch __ro_after_init;
 
 int __cpu_up(unsigned int cpu, struct task_struct *idle)
 {
@@ -138,10 +137,6 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 
 		if (!cpu_online(cpu)) {
 			pr_crit("CPU%u: failed to come online\n", cpu);
-
-			if (IS_ENABLED(CONFIG_ARM64_USER_VA_BITS_52) && va52mismatch)
-				pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
-
 			ret = -EIO;
 		}
 	} else {
@@ -156,7 +151,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 		if (status == CPU_MMU_OFF)
 			status = READ_ONCE(__early_cpu_boot_status);
 
-		switch (status) {
+		switch (status & CPU_BOOT_STATUS_MASK) {
 		default:
 			pr_err("CPU%u: failed in unknown state : 0x%lx\n",
 					cpu, status);
@@ -170,6 +165,10 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 			pr_crit("CPU%u: may not have shut down cleanly\n", cpu);
 		case CPU_STUCK_IN_KERNEL:
 			pr_crit("CPU%u: is stuck in kernel\n", cpu);
+			if (status & CPU_STUCK_REASON_52_BIT_VA)
+				pr_crit("CPU%u: does not support 52-bit VAs\n", cpu);
+			if (status & CPU_STUCK_REASON_NO_GRAN)
+				pr_crit("CPU%u: does not support %luK granule \n", cpu, PAGE_SIZE / SZ_1K);
 			cpus_stuck_in_kernel++;
 			break;
 		case CPU_PANIC_KERNEL: