linux-kernel - Re: [PATCH v5 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master invalidation array

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Message-ID: <aSTfrp9D7i03XhyU@Asurada-Nvidia>
Date: Mon, 24 Nov 2025 14:43:58 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Will Deacon <will@...nel.org>
CC: <jean-philippe@...aro.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<jgg@...dia.com>, <balbirs@...dia.com>, <miko.lenczewski@....com>,
	<peterz@...radead.org>, <kevin.tian@...el.com>, <praan@...gle.com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 4/7] iommu/arm-smmu-v3: Pre-allocate a per-master
 invalidation array

On Mon, Nov 24, 2025 at 09:42:55PM +0000, Will Deacon wrote:
> On Sat, Nov 08, 2025 at 12:08:05AM -0800, Nicolin Chen wrote:
> > +		/* Put the ids into order for sorted to_merge/to_unref arrays */
> > +		sort_nonatomic(fwspec->ids, fwspec->num_ids,
> > +			       sizeof(fwspec->ids[0]), arm_smmu_ids_cmp, NULL);
> > +		/* ATS case adds num_ids of entries, on top of the base case */
> > +		master->build_invs = arm_smmu_invs_alloc(2 + fwspec->num_ids);
> 
> Although I can't point at a specific issue here, I'm nervous about mutating
> the 'fwspec->ids' array from within the driver, The array isn't allocated
> or populated directly by the driver and so I don't think we really have any
> business sorting it. Could we hack iommu_fwspec_add_ids() to keep the array
> ordered instead?

Yea, I think it makes sense to do it in the core, once we have the
data structure provided by the core as well.

Thanks
Nicolin