Hi Nathan,
On Sat, Aug 08, 2015 at 03:03:23AM +0100, Nathan Lynch wrote:
> 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;
Looks good,
Acked-by: Will Deacon <will.dea...@arm.com>
There's probably still time for Catalin to pick this up for 4.2.
Will
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