linux-kernel - Re: [PATCH 0/7] iommu cleanup and refactoring

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Date:   Wed, 26 Jan 2022 09:27:31 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Robin Murphy <robin.murphy@....com>,
        "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>,
        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 0/7] iommu cleanup and refactoring

On Wed, Jan 26, 2022 at 09:51:36AM +0800, Lu Baolu wrote:

> > > they are fundamentally different things in their own right, and the ideal
> > > API should give us the orthogonality to also bind a device to an SVA domain
> > > without PASID (e.g. for KVM stage 2, or userspace assignment of simpler
> > > fault/stall-tolerant devices), or attach PASIDs to regular iommu_domains.
> > 
> > Yes, these are orthogonal things. A iommu driver that supports PASID
> > ideally should support PASID enabled attach/detatch for every
> > iommu_domain type it supports.
> > 
> > SVA should not be entangled with PASID beyond that SVA is often used
> > with PASID - a SVA iommu_domain should be fully usable with a RID too.
> 
> The prototype of PASID enabled attach/detach ops could look like:
> 
>        int (*attach_dev_pasid)(struct iommu_domain *domain,
>                                struct device *dev, ioasid_t id);
>        void (*detach_dev_pasid)(struct iommu_domain *domain,
>                                 struct device *dev, ioasid_t id);

It seems reasonable and straightforward to me..

These would be domain ops?
 
> But the iommu driver should implement different callbacks for
> 
> 1) attaching an IOMMU DMA domain to a PASID on device;
>    - kernel DMA with PASID
>    - mdev-like device passthrough
>    - etc.
> 2) attaching a CPU-shared domain to a PASID on device;
>    - SVA
>    - guest PASID
>    - etc.

But this you mean domain->ops would be different? Seems fine, up to
the driver.

I'd hope to see some flow like:

 domain = device->bus->iommu_ops->alloc_sva_domain(dev)
 domain->ops->attach_dev_pasid(domain, dev, current->pasid)

To duplicate the current SVA APIs

Jason