linux-kernel - Re: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev

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Message-ID: <20250819125249.GG802098@nvidia.com>
Date: Tue, 19 Aug 2025 09:52:49 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: robin.murphy@....com, joro@...tes.org, bhelgaas@...gle.com,
	will@...nel.org, robin.clark@....qualcomm.com, yong.wu@...iatek.com,
	matthias.bgg@...il.com, angelogioacchino.delregno@...labora.com,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	rafael@...nel.org, lenb@...nel.org, kevin.tian@...el.com,
	yi.l.liu@...el.com, baolu.lu@...ux.intel.com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-mediatek@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
	patches@...ts.linux.dev, pjaroszynski@...dia.com, vsethi@...dia.com,
	helgaas@...nel.org, etzhao1900@...il.com
Subject: Re: [PATCH v3 3/5] iommu: Add iommu_get_domain_for_dev_locked()
 helper

On Mon, Aug 18, 2025 at 10:09:11PM -0700, Nicolin Chen wrote:
> Yes, I've thought about that. The concern is that some other place
> someday may want to use iommu_get_domain_for_dev() in similar cases
> but would find that it doesn't work. So it would have to duplicate
> the domain pointer in its "master" structure.
> 
> Overall, having a _locked version feels cleaner to me.

We probably need the locked version, but it just shouldn't be called very
much..

> > With sensible internal locking
> 
> Hmm, I feel this iommu_get_translation_mode() is somewhat the same
> as the current iommu_get_domain_for_dev(). It would just return the
> group->domain->type v.s. group->domain, right?
> 
> This doesn't have any UAF concern though.

Yes, no UAF concern is the point

> > So that is another bunch. Not sure what will be left after.
> 
> I recall that some of the drivers manages their own domains, e.g.
>     drivers/gpu/drm/tegra/drm.c
> 
> So, they would want more out of the domain pointer than just type.

This looks like it wants an 'is currently attached' operation

Jason