clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL

commit e7d65e40ab5a5940785c5922f317602d0268caaf upstream.

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@vger.kernel.org
Signed-off-by: Walter Chang <walter.chang@mediatek.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230717090735.19370-1-walter.chang@mediatek.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 933bb960490d0a287e04e2a648e15cfd9f4fbf85..239c70ac120e821069010cf60c25d697b507a29f 100644 (file)
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -773,6 +773,13 @@ 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;