Subject: Re: [PATCH 2/3] mm/mmu_gather: send tlb_remove_table_smp_sync IPI only to MM CPUs

From: Peter Zijlstra <[email-masked]>
Date: Tue, 4 Apr 2023 16:57:51 +0200

On Tue, Apr 04, 2023 at 04:42:23PM +0300, Yair Podemsky wrote:
> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> index 2b93cf6ac9ae..5ea9be6fb87c 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -191,7 +191,13 @@ static void tlb_remove_table_smp_sync(void *arg)
>  	/* Simply deliver the interrupt */
>  }
>  
> -void tlb_remove_table_sync_one(void)
> +#ifdef CONFIG_ARCH_HAS_CPUMASK_BITS
> +#define REMOVE_TABLE_IPI_MASK mm_cpumask(mm)
> +#else
> +#define REMOVE_TABLE_IPI_MASK NULL
> +#endif /* CONFIG_ARCH_HAS_CPUMASK_BITS */
> +
> +void tlb_remove_table_sync_one(struct mm_struct *mm)
>  {
>  	/*
>  	 * This isn't an RCU grace period and hence the page-tables cannot be
> @@ -200,7 +206,8 @@ void tlb_remove_table_sync_one(void)
>  	 * It is however sufficient for software page-table walkers that rely on
>  	 * IRQ disabling.
>  	 */
> -	smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
> +	on_each_cpu_mask(REMOVE_TABLE_IPI_MASK, tlb_remove_table_smp_sync,
> +			NULL, true);
>  }

Uhh, I don't think NULL is a valid @mask argument. Should that not be
something like:

#ifdef CONFIG_ARCH_HAS_CPUMASK
#define REMOVE_TABLE_IPI_MASK mm_cpumask(mm)
#else
#define REMOVE_TABLE_IPI_MASK cpu_online_mask
#endif

	preempt_disable();
	on_each_cpu_mask(REMOVE_TABLE_IPI_MASK, tlb_remove_table_smp_sync, NULL true);
	preempt_enable();

?