linux-kernel - Re: [PATCH v1 4/4] iommu/arm-smmu-v3-iommufd: Allow a shared s2

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Message-ID: <20250305165743.GA133783@nvidia.com>
Date: Wed, 5 Mar 2025 12:57:43 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
Cc: Nicolin Chen <nicolinc@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"joro@...tes.org" <joro@...tes.org>,
	"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>
Subject: Re: [PATCH v1 4/4] iommu/arm-smmu-v3-iommufd: Allow a shared
 s2_parent to allocate vSMMU

On Wed, Mar 05, 2025 at 09:01:40AM +0000, Shameerali Kolothum Thodi wrote:

> >  	if (!(smmu->features & ARM_SMMU_FEAT_NESTING))
> >  		return ERR_PTR(-EOPNOTSUPP);
> > 
> > -	if (s2_parent->smmu != master->smmu)
> > -		return ERR_PTR(-EINVAL);
> > -
> 
> Not sure we can just relax this like this. What if the two physical SMMUs are different in
> functionality/features? Do we need some kind of sanity check here?

Yes, a function to check if a domain's iopgtbl config is compatible
with the instance is required.

Jason