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

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Message-ID: <20220124163302.GC966497@nvidia.com>
Date:   Mon, 24 Jan 2022 12:33:02 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.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>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Thierry Reding <thierry.reding@...il.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH 7/7] iommu: Add iommu_domain::domain_ops

On Mon, Jan 24, 2022 at 10:16:07AM +0000, Jean-Philippe Brucker wrote:
> On Mon, Jan 24, 2022 at 09:58:18AM +0000, 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)?
> > 
> > Other examples include:
> > 	@apply_resv_region
> > 	@is_attach_deferred
> 
> Could attach_dev() be an IOMMU op?  So a driver could set the domain ops
> in attach_dev() rather than domain_alloc(). That would allow to install
> map()/unmap() ops that are tailored for the device's IOMMU, which we don't
> know at domain_alloc() time. 

I think we should be moving toward 'domain_alloc' returning the
correct domain and the way the driver implements the domain shouldn't
change after that.

> I'm thinking about a guest that has both physical and virtual
> endpoints, which would ideally use different kinds of domain ops to
> support both efficiently (caching mode vs page tables)

In this case shouldn't domain_alloc() reached from the struct device
already do the correct thing?

Jason