ARM: 7787/1: virt: ensure visibility of __boot_cpu_mode

Secondary CPUs write to __boot_cpu_mode with caches disabled, and thus a
cached value of __boot_cpu_mode may be incoherent with that in memory.
This could lead to a failure to detect mismatched boot modes.

This patch adds flushing to ensure that writes by secondaries to
__boot_cpu_mode are made visible before we test against it.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <cdall@cs.columbia.edu>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/virt.h

@@ -29,6 +29,7 @@
 #define BOOT_CPU_MODE_MISMATCH	PSR_N_BIT
 
 #ifndef __ASSEMBLY__
+#include <asm/cacheflush.h>
 
 #ifdef CONFIG_ARM_VIRT_EXT
 /*
@@ -41,10 +42,21 @@
  */
 extern int __boot_cpu_mode;
 
+static inline void sync_boot_mode(void)
+{
+	/*
+	 * As secondaries write to __boot_cpu_mode with caches disabled, we
+	 * must flush the corresponding cache entries to ensure the visibility
+	 * of their writes.
+	 */
+	sync_cache_r(&__boot_cpu_mode);
+}
+
 void __hyp_set_vectors(unsigned long phys_vector_base);
 unsigned long __hyp_get_vectors(void);
 #else
 #define __boot_cpu_mode	(SVC_MODE)
+#define sync_boot_mode()
 #endif
 
 #ifndef ZIMAGE

arch/arm/kernel/setup.c

@@ -836,6 +836,8 @@ static int __init meminfo_cmp(const void *_a, const void *_b)
 void __init hyp_mode_check(void)
 {
 #ifdef CONFIG_ARM_VIRT_EXT
+	sync_boot_mode();
+
 	if (is_hyp_mode_available()) {
 		pr_info("CPU: All CPU(s) started in HYP mode.\n");
 		pr_info("CPU: Virtualization extensions available.\n");