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arm64: vdso: Fix clock_getres() for CLOCK_REALTIME

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clock_getres() in the vDSO library has to preserve the same behaviour
of posix_get_hrtimer_res().

In particular, posix_get_hrtimer_res() does:

    sec = 0;
    ns = hrtimer_resolution;

where 'hrtimer_resolution' depends on whether or not high resolution
timers are enabled, which is a runtime decision.

The vDSO incorrectly returns the constant CLOCK_REALTIME_RES. Fix this
by exposing 'hrtimer_resolution' in the vDSO datapage and returning that
instead.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
[will: Use WRITE_ONCE(), move adr off COARSE path, renumber labels, use 'w' reg]
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Vincenzo Frascino
2019-04-16 17:14:30 +01:00
committed by Will Deacon
parent 22e6c8087e
commit 81fb8736dd
4 changed files with 8 additions and 5 deletions
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1
arch/arm64/include/asm/vdso_datapage.h
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@@ -38,6 +38,7 @@ struct vdso_data {
__u32 tz_minuteswest; /* Whacky timezone stuff */
__u32 tz_dsttime;
__u32 use_syscall;
__u32 hrtimer_res;
};
#endif /* !__ASSEMBLY__ */

2
arch/arm64/kernel/asm-offsets.c
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@@ -94,7 +94,7 @@ int main(void)
DEFINE(CLOCK_REALTIME, CLOCK_REALTIME);
DEFINE(CLOCK_MONOTONIC, CLOCK_MONOTONIC);
DEFINE(CLOCK_MONOTONIC_RAW, CLOCK_MONOTONIC_RAW);
DEFINE(CLOCK_REALTIME_RES, MONOTONIC_RES_NSEC);
DEFINE(CLOCK_REALTIME_RES, offsetof(struct vdso_data, hrtimer_res));
DEFINE(CLOCK_REALTIME_COARSE, CLOCK_REALTIME_COARSE);
DEFINE(CLOCK_MONOTONIC_COARSE,CLOCK_MONOTONIC_COARSE);
DEFINE(CLOCK_COARSE_RES, LOW_RES_NSEC);

3
arch/arm64/kernel/vdso.c
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@@ -230,6 +230,9 @@ void update_vsyscall(struct timekeeper *tk)
vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec;
vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec;
/* Read without the seqlock held by clock_getres() */
WRITE_ONCE(vdso_data->hrtimer_res, hrtimer_resolution);
if (!use_syscall) {
/* tkr_mono.cycle_last == tkr_raw.cycle_last */
vdso_data->cs_cycle_last = tk->tkr_mono.cycle_last;

7
arch/arm64/kernel/vdso/gettimeofday.S
View File

@@ -301,13 +301,14 @@ ENTRY(__kernel_clock_getres)
ccmp w0, #CLOCK_MONOTONIC_RAW, #0x4, ne
b.ne 1f
ldr x2, 5f
adr vdso_data, _vdso_data
ldr w2, [vdso_data, #CLOCK_REALTIME_RES]
b 2f
1:
cmp w0, #CLOCK_REALTIME_COARSE
ccmp w0, #CLOCK_MONOTONIC_COARSE, #0x4, ne
b.ne 4f
ldr x2, 6f
ldr x2, 5f
2:
cbz x1, 3f
stp xzr, x2, [x1]
@@ -321,8 +322,6 @@ ENTRY(__kernel_clock_getres)
svc #0
ret
5:
.quad CLOCK_REALTIME_RES
6:
.quad CLOCK_COARSE_RES
.cfi_endproc
ENDPROC(__kernel_clock_getres)