linux-kernel - Re: [PATCH v2 02/10] iommu: Introduce a new iommu_group_replace

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Message-ID: <Y+Tzt0p+hDz0QMfH@nvidia.com>
Date:   Thu, 9 Feb 2023 09:23:03 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Nicolin Chen <nicolinc@...dia.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "will@...nel.org" <will@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v2 02/10] iommu: Introduce a new
 iommu_group_replace_domain() API

On Thu, Feb 09, 2023 at 02:55:24AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Wednesday, February 8, 2023 5:18 AM
> > 
> > +int iommu_group_replace_domain(struct iommu_group *group,
> > +			       struct iommu_domain *new_domain)
> > +{
> > +	int ret;
> > +
> > +	if (!new_domain)
> > +		return -EINVAL;
> 
> Is there value of allowing NULL new domain so this plays like
> iommu_detach_group() then iommufd only needs call one
> function in both attach/detach path?

We've used NULL to mean the 'platform domain' in the iommu core code
in a few places, I'd prefer to avoid overloading NULL.

IMHO it doesn't help iommufd to substitute detach with replace.

Jason