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arm64: Fix __arch_get_hw_counter() implementation

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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.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mips@vger.kernel.org
Cc: linux-kselftest@vger.kernel.org
Cc: catalin.marinas@arm.com
Cc: will.deacon@arm.com
Cc: arnd@arndb.de
Cc: linux@armlinux.org.uk
Cc: ralf@linux-mips.org
Cc: paul.burton@mips.com
Cc: daniel.lezcano@linaro.org
Cc: salyzyn@android.com
Cc: pcc@google.com
Cc: shuah@kernel.org
Cc: 0x7f454c46@gmail.com
Cc: linux@rasmusvillemoes.dk
Cc: huw@codeweavers.com
Cc: sthotton@marvell.com
Cc: andre.przywara@arm.com
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20190625161804.38713-2-vincenzo.frascino@arm.com
This commit is contained in:
Vincenzo Frascino 2019-06-25 17:18:03 +01:00 committed by Thomas Gleixner
parent 9d90b93bf3
commit 27e11a9fe2
1 changed files with 19 additions and 0 deletions
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19
arch/arm64/include/asm/vdso/gettimeofday.h
View File

@ -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;
}