linux-kernel - Re: [PATCH v3 20/29] arm_mpam: Allow configuration to be applied and restored during cpu online

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Message-ID: <9ad95fa5-6f1d-4c31-a6c6-41c1e9cc5c20@arm.com>
Date: Mon, 20 Oct 2025 18:04:28 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Dave Martin <dave.martin@....com>,
 Koba Ko <kobak@...dia.com>, Shanker Donthineni <sdonthineni@...dia.com>,
 fenghuay@...dia.com, baisheng.gao@...soc.com,
 Jonathan Cameron <jonathan.cameron@...wei.com>, Rob Herring
 <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>, Jeremy Linton <jeremy.linton@....com>,
 Gavin Shan <gshan@...hat.com>
Subject: Re: [PATCH v3 20/29] arm_mpam: Allow configuration to be applied and
 restored during cpu online

Hi James,

On 10/17/25 19:56, James Morse wrote:
> When CPUs come online the MSC's original configuration should be restored.
> 
> Add struct mpam_config to hold the configuration. This has a bitmap of
> features that were modified. Once the maximum partid is known, allocate
> a configuration array for each component, and reprogram each RIS
> configuration from this.
> 
> CC: Dave Martin <Dave.Martin@....com>
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Reviewed-by: Ben Horgan <ben.horgan@....com>
> Tested-by: Fenghua Yu <fenghuay@...dia.com>
> ---
> Changes since v2:
>  * Call mpam_init_reset_cfg() on alloated config as 0 is not longer correct.
>  * init_garbage() on each config - the array has to be freed in one go, but
>    otherwise this looks weird.
>  * Use struct initialiser in mpam_init_reset_cfg(),
>  * Moved int err definition.
>  * Removed srcu lock taking based on squinting at the only caller.
>  * Moved config reset to mpam_reset_component_cfg() for re-use in
>    mpam_reset_component_locked(), previous memset() was not enough since zero
>    no longer means reset.
> 
[...]
>  
> +struct reprogram_ris {
> +	struct mpam_msc_ris *ris;
> +	struct mpam_config *cfg;
> +};
> +
> +/* Call with MSC lock held */
> +static int mpam_reprogram_ris(void *_arg)
> +{
> +	u16 partid, partid_max;
> +	struct reprogram_ris *arg = _arg;
> +	struct mpam_msc_ris *ris = arg->ris;
> +	struct mpam_config *cfg = arg->cfg;
> +
> +	if (ris->in_reset_state)
> +		return 0;
> +
> +	spin_lock(&partid_max_lock);
> +	partid_max = mpam_partid_max;
> +	spin_unlock(&partid_max_lock);
> +	for (partid = 0; partid <= partid_max + 1; partid++)

Loop overrun. This was correct in the previous version of the patch and
the same shape of loop is done correctly elsewhere in this version. I
think it would be good to standardise on using either:
partid <= partid_max
or
partid < partid_max + 1
I have a preference for the first as you don't need to think about the
size of the type.

-- 
Thanks,

Ben