Re: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid structures by index

[James Morse <james.morse@arm.com>]

Hi Amit,

On 31/10/2023 07:43, Amit Singh Tomar wrote:
> -----Original Message-----
> From: James Morse <james.morse@arm.com> 
> Sent: Wednesday, October 25, 2023 11:33 PM
> Subject: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid structures by index

Looks like you are afflicted with outlook - let me know if I didn't find all the changes
you made to the original message ...

[..]

> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> index 2a0233cd0bc9..c02cf32cd17c 100644
> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> @@ -735,19 +768,20 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
>  
>  static int dom_data_init(struct rdt_resource *r)  {
> +	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
>  	struct rmid_entry *entry = NULL;
> -	int i, nr_rmids;
> +	u32 idx;
> +	int i;
>  
> -	nr_rmids = r->num_rmid;
> -	rmid_ptrs = kcalloc(nr_rmids, sizeof(struct rmid_entry), GFP_KERNEL);
> +	rmid_ptrs = kcalloc(idx_limit, sizeof(struct rmid_entry), GFP_KERNEL);
> 
> [>>] Is there a chance, it could result in "ZERO_SIZE_PTR", and we should guard it against ZERO_OR_NULL_PTR in the following if condition?
>         It might be related, while testing the snapshot[1] (and subsequent snapshots has similar change) on x86 platform, Zahid is seeing Kernel panic:
>         https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/tree/fs/resctrl/monitor.c?h=mpam/snapshot/v6.2#n695

Interesting - I didn't think this could happen. Could you share the full splat?

This would imply idx_limit was zero, so boot_cpu_data.x86_cache_max_rmid would be -1.
But wouldn't this happen before this patch? idx_limit has the same value as nr_rmids on
x86, its only MPAM that needs a different value.


Thanks,

James