Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL

[Marc Zyngier]

On Mon, 17 Jul 2023 10:07:34 +0100,
<walter.chang@xxxxxxxxxxxx> wrote:
> 
> From: Walter Chang <walter.chang@xxxxxxxxxxxx>
> 
> Due to the fact that the use of `writeq_relaxed()` to program CVAL is
> not guaranteed to be atomic, it is necessary to disable the timer before
> programming CVAL.
> 
> However, if the MMIO timer is already enabled and has not yet expired,
> there is a possibility of unexpected behavior occurring: when the CPU
> enters the idle state during this period, and if the CPU's local event
> is earlier than the broadcast event, the following process occurs:
> 
> tick_broadcast_enter()
>   tick_broadcast_oneshot_control(TICK_BROADCAST_ENTER)
>     __tick_broadcast_oneshot_control()
>       ___tick_broadcast_oneshot_control()
>         tick_broadcast_set_event()
>           clockevents_program_event()
>             set_next_event_mem()
> 
> During this process, the MMIO timer remains enabled while programming
> CVAL. To prevent such behavior, disable timer explicitly prior to
> programming CVAL.
> 
> Fixes: 8b82c4f883a7 ("clocksource/drivers/arm_arch_timer: Move MMIO timer programming over to CVAL")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Walter Chang <walter.chang@xxxxxxxxxxxx>

Acked-by: Marc Zyngier <maz@xxxxxxxxxx>

	M.

-- 
Without deviation from the norm, progress is not possible.