linux-kernel - Re: [PATCH 2/5] iommu: Add blocking_domain_ops field in iommu

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Date:   Tue, 17 May 2022 10:13:24 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] iommu: Add blocking_domain_ops field in iommu_ops

On Tue, May 17, 2022 at 01:43:03PM +0100, Robin Murphy wrote:

> FWIW from my point of view I'm happy with having a .detach_dev_pasid op
> meaning implicitly-blocked access for now. 

If this is the path then lets not call it attach/detach
please. 'set_dev_pasid' and 'set_dev_blocking_pasid' are clearer
names.

> On SMMUv3, PASIDs don't mix with our current notion of
> IOMMU_DOMAIN_IDENTITY (nor the potential one for
> IOMMU_DOMAIN_BLOCKED), so giving PASIDs functional symmetry with
> devices would need significantly more work anyway.

There is no extra work in the driver, beyond SMMU having to implement
a blocking domain. The blocking domain's set_dev_pasid op simply is
whatever set_dev_blocking_pasid would have done on the unmanaged
domain.

identity doesn't come into this, identity domains should have a NULL
set_dev_pasid op if the driver can't support using it on a PASID.

IMHO blocking_domain->ops->set_dev_pasid() is just a more logical name
than domain->ops->set_dev_blocking_pasid() - especially since VFIO
would like drivers to implement blocking domain anyhow.

Jason