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arm64: compat: 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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
This commit is contained in:
Vincenzo Frascino 2019-06-25 17:18:04 +01:00 • committed by Thomas Gleixner
commit 6241c4dc6e
1 changed files with 18 additions and 0 deletions
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18
arch/arm64/include/asm/vdso/compat_gettimeofday.h
View file

@ -12,6 +12,8 @@
#include <asm/vdso/compat_barrier.h>
#define __VDSO_USE_SYSCALL ULLONG_MAX
#define VDSO_HAS_CLOCK_GETRES 1
static __always_inline
@ -74,8 +76,24 @@ 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("mrrc p15, 1, %Q0, %R0, c14" : "=r" (res));
/*
* This isb() is required to prevent that the seq lock is
* speculated.
*/
isb();
return res;
}