linux-kernel - Re: [PATCH 7/7] iommu: Add iommu_domain::domain

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Date:   Tue, 25 Jan 2022 08:37:29 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops

On Tue, Jan 25, 2022 at 12:59:14PM +0800, Lu Baolu wrote:
> On 1/24/22 5:58 PM, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > > Sent: Monday, January 24, 2022 3:11 PM
> > > +/**
> > > + * struct domain_ops - per-domain ops
> > > + * @attach_dev: attach an iommu domain to a device
> > > + * @detach_dev: detach an iommu domain from a device
> > 
> > What is the criteria about whether an op should be iommu_ops or domain_ops
> > when it requires both domain and device pointers like above two (and future
> > PASID-based attach)?
> 
> Generally ops belong to iommu_ops if they are only device oriented, and
> domain_ops if they are only domain oriented. But it's really hard to
> judge when both device and domain are involved. Good question. :-)
> 
> Perhaps we should leave the attach/detach interfaces in iommu_ops since
> they are related to device capabilities. For example, some devices
> support attach_dev_pasid, while others not.

Isn't the attach process for something like SVA or the KVM version
actually rather different code?

Ideally the function pointers should help minimize case statements/etc
inside the driver..

Or stated another way, I expect drivers will have different structs
container_of'ing back to the iommu_domain (ie intel_iommu_domain_sva,
say). Any code that needs to work differently depending on the struct
should have an op in the domain so it can sanely container_of without
a mess.

Jason