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

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Message-ID: <BN9PR11MB5276CC4AFEA8DFE315BD51C08C74A@BN9PR11MB5276.namprd11.prod.outlook.com>
Date: Thu, 12 Jun 2025 08:22:49 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Nicolin Chen <nicolinc@...dia.com>, Baolu Lu <baolu.lu@...ux.intel.com>
CC: "jgg@...dia.com" <jgg@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>, "joro@...tes.org"
	<joro@...tes.org>, "ddutile@...hat.com" <ddutile@...hat.com>, "Liu, Yi L"
	<yi.l.liu@...el.com>, "peterz@...radead.org" <peterz@...radead.org>,
	"jsnitsel@...hat.com" <jsnitsel@...hat.com>, "praan@...gle.com"
	<praan@...gle.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "patches@...ts.linux.dev"
	<patches@...ts.linux.dev>
Subject: RE: [PATCH v1 08/12] iommufd/viommu: Replace ops->viommu_alloc with
 ops->viommu_init

> From: Nicolin Chen <nicolinc@...dia.com>
> Sent: Tuesday, June 10, 2025 2:20 PM
> 
> 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.
> 

WARN_ON_ONCE() is built on the current context, not the future
usage. So I'd prefer to keeping it until there is a real need to revert.

Reviewed-by: Kevin Tian <kevin.tian@...el.com>