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

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Date:   Mon, 11 Dec 2023 14:33:06 +0000
From:   James Morse <james.morse@....com>
To:     Amit Singh Tomar <amitsinght@...vell.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Babu Moger <Babu.Moger@....com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        D Scott Phillips OS <scott@...amperecomputing.com>,
        "carl@...amperecomputing.com" <carl@...amperecomputing.com>,
        Linu Cherian <lcherian@...vell.com>,
        "bobo.shaobowang@...wei.com" <bobo.shaobowang@...wei.com>,
        "tan.shaopeng@...itsu.com" <tan.shaopeng@...itsu.com>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Xin Hao <xhao@...ux.alibaba.com>,
        "peternewman@...gle.com" <peternewman@...gle.com>,
        "dfustini@...libre.com" <dfustini@...libre.com>,
        "muhammad.zahid@...ia.com" <muhammad.zahid@...ia.com>
Subject: Re: [EXT] [PATCH v7 06/24] x86/resctrl: Access per-rmid structures by
 index

Hi Amit,

On 31/10/2023 07:43, Amit Singh Tomar wrote:
> -----Original Message-----
> From: James Morse <james.morse@....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