From: Walter Chang <[email protected]>
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: [email protected]
Signed-off-by: Walter Chang <[email protected]>
---
drivers/clocksource/arm_arch_timer.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index e733a2a1927a..7dd2c615bce2 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -792,6 +792,13 @@ static __always_inline void set_next_event_mem(const int access, unsigned long e
u64 cnt;
ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
+
+ /* Timer must be disabled before programming CVAL */
+ if (ctrl & ARCH_TIMER_CTRL_ENABLE) {
+ ctrl &= ~ARCH_TIMER_CTRL_ENABLE;
+ arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
+ }
+
ctrl |= ARCH_TIMER_CTRL_ENABLE;
ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
--
2.18.0
On Mon, 17 Jul 2023 10:07:34 +0100,
<[email protected]> wrote:
>
> From: Walter Chang <[email protected]>
>
> 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: [email protected]
> Signed-off-by: Walter Chang <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
M.
--
Without deviation from the norm, progress is not possible.
Il 17/07/23 11:07, [email protected] ha scritto:
> From: Walter Chang <[email protected]>
>
> 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: [email protected]
> Signed-off-by: Walter Chang <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
> ---
> drivers/clocksource/arm_arch_timer.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index e733a2a1927a..7dd2c615bce2 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -792,6 +792,13 @@ static __always_inline void set_next_event_mem(const int access, unsigned long e
> u64 cnt;
>
> ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
> +
> + /* Timer must be disabled before programming CVAL */
> + if (ctrl & ARCH_TIMER_CTRL_ENABLE) {
> + ctrl &= ~ARCH_TIMER_CTRL_ENABLE;
> + arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl, clk);
> + }
> +
> ctrl |= ARCH_TIMER_CTRL_ENABLE;
> ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
>