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Subject[PATCH 4.19 152/276] arm64: vdso: Fix clock_getres() for CLOCK_REALTIME
Date
[ Upstream commit 81fb8736dd81da3fe94f28968dac60f392ec6746 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/include/asm/vdso_datapage.h | 1 +
arch/arm64/kernel/asm-offsets.c | 2 +-
arch/arm64/kernel/vdso.c | 3 +++
arch/arm64/kernel/vdso/gettimeofday.S | 7 +++----
4 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/vdso_datapage.h b/arch/arm64/include/asm/vdso_datapage.h
index 2b9a63771eda8..f89263c8e11af 100644
--- a/arch/arm64/include/asm/vdso_datapage.h
+++ b/arch/arm64/include/asm/vdso_datapage.h
@@ -38,6 +38,7 @@ struct vdso_data {
__u32 tz_minuteswest; /* Whacky timezone stuff */
__u32 tz_dsttime;
__u32 use_syscall;
+ __u32 hrtimer_res;
};

#endif /* !__ASSEMBLY__ */
diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
index 323aeb5f2fe62..92fba851ce53a 100644
--- a/arch/arm64/kernel/asm-offsets.c
+++ b/arch/arm64/kernel/asm-offsets.c
@@ -99,7 +99,7 @@ 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);
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 2d419006ad433..ec0bb588d7553 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -232,6 +232,9 @@ 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;
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index e8f60112818fc..856fee6d35129 100644
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -308,13 +308,14 @@ 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]
@@ -328,8 +329,6 @@ ENTRY(__kernel_clock_getres)
svc #0
ret
5:
- .quad CLOCK_REALTIME_RES
-6:
.quad CLOCK_COARSE_RES
.cfi_endproc
ENDPROC(__kernel_clock_getres)
--
2.20.1


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