linux-kernel - Re: [PATCH v1 08/12] iommufd/viommu: Replace ops->viommu_alloc with ops->viommu

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Message-ID: <aEfOjnj7xGPbfYD4@nvidia.com>
Date: Mon, 9 Jun 2025 23:19:58 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
CC: <jgg@...dia.com>, <kevin.tian@...el.com>, <will@...nel.org>,
	<robin.murphy@....com>, <joro@...tes.org>, <ddutile@...hat.com>,
	<yi.l.liu@...el.com>, <peterz@...radead.org>, <jsnitsel@...hat.com>,
	<praan@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
	<iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v1 08/12] iommufd/viommu: Replace ops->viommu_alloc with
 ops->viommu_init

On Tue, Jun 10, 2025 at 01:55:05PM +0800, Baolu Lu wrote:
> On 6/10/25 01:13, Nicolin Chen wrote:
> > To ease the for-driver iommufd APIs, get_viommu_size and viommu_init ops
> > are introduced. Now, those existing vIOMMU supported drivers implemented
> > these two ops too.
> > 
> > Relace the ops->viommu_alloc call with the two new ones.
> > 
> > Note that this will fail a !viommu->ops case from now on, since a vIOMMU
> > is expected to support alloc_domain_nested at least.
> 
> Does this mean that the viommu implementation in the iommu driver is
> required to implement alloc_domain_nested? I suppose viommu should soon
> be extended to support TEE/IO.

It's a good point that CCA might not need a nested domain. So,
it's inaccurate to say that, although I suspect that CCA would
need some other viommu op then the check here would be sane.

With that being said, it's probably not worth adding that until
we are 100% sure that no case will work with a !viommu->ops, so
let's drop this new rejection, since we haven't had it so far.

Thanks
Nicolin