Re: [PATCH 05/13] clocksource/arm_arch_timer: Fix MMIO base address vs callback ordering issue

[Mark Rutland]

On Mon, Aug 09, 2021 at 04:26:43PM +0100, Marc Zyngier wrote:
> The MMIO timer base address gets published after we have registered
> the callbacks and the interrupt handler, which is... a bit dangerous.
> 
> Fix this by moving the base address publication to the point where
> we register the timer, and expose a pointer to the timer structure
> itself rather than a naked value.
> 
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

I don't have agood setup to test this with, but this looks good to me,
and builds cleanly for arm/arm64, so:

Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>

Mark.

> ---
>  drivers/clocksource/arm_arch_timer.c | 27 +++++++++++++--------------
>  1 file changed, 13 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
> index 160464f75017..ca7761d8459a 100644
> --- a/drivers/clocksource/arm_arch_timer.c
> +++ b/drivers/clocksource/arm_arch_timer.c
> @@ -54,13 +54,13 @@
>  
>  static unsigned arch_timers_present __initdata;
>  
> -static void __iomem *arch_counter_base __ro_after_init;
> -
>  struct arch_timer {
>  	void __iomem *base;
>  	struct clock_event_device evt;
>  };
>  
> +static struct arch_timer *arch_timer_mem __ro_after_init;
> +
>  #define to_arch_timer(e) container_of(e, struct arch_timer, evt)
>  
>  static u32 arch_timer_rate __ro_after_init;
> @@ -975,9 +975,9 @@ static u64 arch_counter_get_cntvct_mem(void)
>  	u32 vct_lo, vct_hi, tmp_hi;
>  
>  	do {
> -		vct_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
> -		vct_lo = readl_relaxed(arch_counter_base + CNTVCT_LO);
> -		tmp_hi = readl_relaxed(arch_counter_base + CNTVCT_HI);
> +		vct_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
> +		vct_lo = readl_relaxed(arch_timer_mem->base + CNTVCT_LO);
> +		tmp_hi = readl_relaxed(arch_timer_mem->base + CNTVCT_HI);
>  	} while (vct_hi != tmp_hi);
>  
>  	return ((u64) vct_hi << 32) | vct_lo;
> @@ -1168,25 +1168,25 @@ static int __init arch_timer_mem_register(void __iomem *base, unsigned int irq)
>  {
>  	int ret;
>  	irq_handler_t func;
> -	struct arch_timer *t;
>  
> -	t = kzalloc(sizeof(*t), GFP_KERNEL);
> -	if (!t)
> +	arch_timer_mem = kzalloc(sizeof(*arch_timer_mem), GFP_KERNEL);
> +	if (!arch_timer_mem)
>  		return -ENOMEM;
>  
> -	t->base = base;
> -	t->evt.irq = irq;
> -	__arch_timer_setup(ARCH_TIMER_TYPE_MEM, &t->evt);
> +	arch_timer_mem->base = base;
> +	arch_timer_mem->evt.irq = irq;
> +	__arch_timer_setup(ARCH_TIMER_TYPE_MEM, &arch_timer_mem->evt);
>  
>  	if (arch_timer_mem_use_virtual)
>  		func = arch_timer_handler_virt_mem;
>  	else
>  		func = arch_timer_handler_phys_mem;
>  
> -	ret = request_irq(irq, func, IRQF_TIMER, "arch_mem_timer", &t->evt);
> +	ret = request_irq(irq, func, IRQF_TIMER, "arch_mem_timer", &arch_timer_mem->evt);
>  	if (ret) {
>  		pr_err("Failed to request mem timer irq\n");
> -		kfree(t);
> +		kfree(arch_timer_mem);
> +		arch_timer_mem = NULL;
>  	}
>  
>  	return ret;
> @@ -1444,7 +1444,6 @@ arch_timer_mem_frame_register(struct arch_timer_mem_frame *frame)
>  		return ret;
>  	}
>  
> -	arch_counter_base = base;
>  	arch_timers_present |= ARCH_TIMER_TYPE_MEM;
>  
>  	return 0;
> -- 
> 2.30.2
>