Since 906c55579a63 ("timekeeping: Copy the shadow-timekeeper over the
real timekeeper last") it has become possible on arm64 to:
- Obtain a CLOCK_MONOTONIC_COARSE or CLOCK_REALTIME_COARSE timestamp
via syscall.
- Subsequently obtain a timestamp for the same clock ID via VDSO which
predates the first timestamp (by one jiffy).
This is because arm64's update_vsyscall is deriving the coarse time
using the __current_kernel_time interface, when it should really be
using the timekeeper object provided to it by the timekeeping core.
It happened to work before only because __current_kernel_time would
access the same timekeeper object which had been passed to
update_vsyscall. This is no longer the case.
Signed-off-by: Nathan Lynch <nathan_ly...@mentor.com>
---
arch/arm64/kernel/vdso.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index ec37ab3f524f..97bc68f4c689 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -199,16 +199,15 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
*/
void update_vsyscall(struct timekeeper *tk)
{
- struct timespec xtime_coarse;
u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");
++vdso_data->tb_seq_count;
smp_wmb();
- xtime_coarse = __current_kernel_time();
vdso_data->use_syscall = use_syscall;
- vdso_data->xtime_coarse_sec = xtime_coarse.tv_sec;
- vdso_data->xtime_coarse_nsec = xtime_coarse.tv_nsec;
+ vdso_data->xtime_coarse_sec = tk->xtime_sec;
+ vdso_data->xtime_coarse_nsec = tk->tkr_mono.xtime_nsec >>
+ tk->tkr_mono.shift;
vdso_data->wtm_clock_sec = tk->wall_to_monotonic.tv_sec;
vdso_data->wtm_clock_nsec = tk->wall_to_monotonic.tv_nsec;
--
2.1.0
--
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