Provide the following fixes for the __arch_get_hw_counter() implementation on arm64: - Fallback on syscall when an unstable counter is detected. - Introduce isb()s before and after the counter read to avoid speculation of the counter value and of the seq lock respectively. The second isb() is a temporary solution that will be revisited in 5.3-rc1.
These fixes restore the semantics that __arch_counter_get_cntvct() had on arm64.
Cc: Catalin Marinas catalin.marinas@arm.com Cc: Will Deacon will.deacon@arm.com Signed-off-by: Vincenzo Frascino vincenzo.frascino@arm.com --- arch/arm64/include/asm/vdso/gettimeofday.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/arch/arm64/include/asm/vdso/gettimeofday.h b/arch/arm64/include/asm/vdso/gettimeofday.h index 447ef417de45..b08f476b72b4 100644 --- a/arch/arm64/include/asm/vdso/gettimeofday.h +++ b/arch/arm64/include/asm/vdso/gettimeofday.h @@ -10,6 +10,8 @@ #include <asm/unistd.h> #include <uapi/linux/time.h>
+#define __VDSO_USE_SYSCALL ULLONG_MAX + #define VDSO_HAS_CLOCK_GETRES 1
static __always_inline @@ -68,7 +70,24 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode) { u64 res;
+ /* + * clock_mode == 0 implies that vDSO are enabled otherwise + * fallback on syscall. + */ + if (clock_mode) + return __VDSO_USE_SYSCALL; + + /* + * This isb() is required to prevent that the counter value + * is speculated. + */ + isb(); asm volatile("mrs %0, cntvct_el0" : "=r" (res) :: "memory"); + /* + * This isb() is required to prevent that the seq lock is + * speculated.# + */ + isb();
return res; }