arm64: ensure CPU clock retrieval issues isb()

This prevents counter value speculation, which will otherwise cause
issues with the CPU clock.

Link: https://github.com/axboe/fio/issues/1472
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/arch/arch-aarch64.h b/arch/arch-aarch64.h
index 951d1718cfabfbe59469c3421b67d4bc8fb5e103..919e57967609b4b077c50396c5aaf0cc6f4a1d05 100644 (file)
--- a/arch/arch-aarch64.h
+++ b/arch/arch-aarch64.h
@@ -27,10 +27,13 @@ static inline int arch_ffz(unsigned long bitmask)
 
 #define ARCH_HAVE_FFZ
 
+#define isb()  asm volatile("isb" : : : "memory")
+
 static inline unsigned long long get_cpu_clock(void)
 {
        unsigned long val;
 
+       isb();
        asm volatile("mrs %0, cntvct_el0" : "=r" (val));
        return val;
 }