On Thu, Aug 11, 2016 at 11:37:44AM -0400, Christopher Covington wrote:
> From: Brent DeGraaf <bdegr...@codeaurora.org>
>
> Prior gettimeofday code register read code is not architecturally
> correct as there is no control flow gating logic enforced
> immediately prior to the required isb. Introduce explicit
> control-flow logic prior to register read in all cases so that
> the mrs read will always be done after all vdso data elements are
> read, and read all data elements within the protection logic
> provided by the sequence counter.
-ENOPARSE
Can you explain the problem that you're fixing here, please?
> Signed-off-by: Brent DeGraaf <bdegr...@codeaurora.org>
> ---
> arch/arm64/include/asm/vdso_datapage.h | 4 +-
> arch/arm64/kernel/vdso.c | 11 ++--
> arch/arm64/kernel/vdso/gettimeofday.S | 106
> +++++++++++++++------------------
> 3 files changed, 56 insertions(+), 65 deletions(-)
>
> diff --git a/arch/arm64/include/asm/vdso_datapage.h
> b/arch/arm64/include/asm/vdso_datapage.h
> index 2b9a637..49a0a51 100644
> --- a/arch/arm64/include/asm/vdso_datapage.h
> +++ b/arch/arm64/include/asm/vdso_datapage.h
> @@ -21,6 +21,8 @@
> #ifndef __ASSEMBLY__
>
> struct vdso_data {
> + __u32 tb_seq_count; /* Timebase sequence counter */
> + __u32 use_syscall;
> __u64 cs_cycle_last; /* Timebase at clocksource init */
> __u64 raw_time_sec; /* Raw time */
> __u64 raw_time_nsec;
> @@ -30,14 +32,12 @@ struct vdso_data {
> __u64 xtime_coarse_nsec;
> __u64 wtm_clock_sec; /* Wall to monotonic time */
> __u64 wtm_clock_nsec;
> - __u32 tb_seq_count; /* Timebase sequence counter */
> /* cs_* members must be adjacent and in this order (ldp accesses) */
> __u32 cs_mono_mult; /* NTP-adjusted clocksource multiplier */
> __u32 cs_shift; /* Clocksource shift (mono = raw) */
> __u32 cs_raw_mult; /* Raw clocksource multiplier */
> __u32 tz_minuteswest; /* Whacky timezone stuff */
> __u32 tz_dsttime;
> - __u32 use_syscall;
> };
>
> #endif /* !__ASSEMBLY__ */
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index 076312b..7751667 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -201,10 +201,12 @@ up_fail:
> */
> void update_vsyscall(struct timekeeper *tk)
> {
> + register u32 tmp;
> u32 use_syscall = strcmp(tk->tkr_mono.clock->name, "arch_sys_counter");
>
> - ++vdso_data->tb_seq_count;
> - smp_wmb();
> + tmp = smp_load_acquire(&vdso_data->tb_seq_count);
> + ++tmp;
> + smp_store_release(&vdso_data->tb_seq_count, tmp);
This looks busted -- the writes to vdso_data can be reordered before the
update of tb_seq_count.
/confused
Will
