arm64: 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>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <cdall@cs.columbia.edu>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
index 439827271e3d..26e310c54344 100644
--- a/arch/arm64/include/asm/virt.h
+++ b/arch/arm64/include/asm/virt.h
@@ -21,6 +21,7 @@
 #define BOOT_CPU_MODE_EL2       (0x0e12b007)
 
 #ifndef __ASSEMBLY__
+#include <asm/cacheflush.h>
 
 /*
  * __boot_cpu_mode records what mode CPUs were booted in.
@@ -36,9 +37,20 @@ extern u32 __boot_cpu_mode[2];
 void __hyp_set_vectors(phys_addr_t phys_vector_base);
 phys_addr_t __hyp_get_vectors(void);
 
+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.
+         */
+        __flush_dcache_area(__boot_cpu_mode, sizeof(__boot_cpu_mode));
+}
+
 /* Reports the availability of HYP mode */
 static inline bool is_hyp_mode_available(void)
 {
+        sync_boot_mode();
         return (__boot_cpu_mode[0] == BOOT_CPU_MODE_EL2 &&
                 __boot_cpu_mode[1] == BOOT_CPU_MODE_EL2);
 }
@@ -46,6 +58,7 @@ static inline bool is_hyp_mode_available(void)
 /* Check if the bootloader has booted CPUs in different modes */
 static inline bool is_hyp_mode_mismatched(void)
 {
+        sync_boot_mode();
         return __boot_cpu_mode[0] != __boot_cpu_mode[1];
 }