linux-kernel - Re: [PATCH RFC v2 03/11] iommu/sva: Add iommu

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Message-ID: <20220406012334.GZ2120790@nvidia.com>
Date:   Tue, 5 Apr 2022 22:23:34 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v2 03/11] iommu/sva: Add iommu_domain type for SVA

On Wed, Apr 06, 2022 at 01:00:13AM +0000, Tian, Kevin wrote:

> > Because domains wrap more than just the IOPTE format, they have
> > additional data related to the IOMMU HW block itself. Imagine a SOC
> > with two IOMMU HW blocks that can both process the CPU IOPTE format,
> > but have different configuration.
> 
> Curious. Is it hypothesis or real? If real can you help give a concrete
> example?

Look at arm_smmu_attach_dev() - the domain has exactly one smmu
pointer which contains the base address for the SMMU IP block. If the
domain doesn't match the smmu pointer from the struct device it won't
allow attaching.

I know of ARM SOCs with many copies of the SMMU IP block.

So at least with current drivers ARM seems to have this limitation.

Jason