linux-kernel - Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev

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Message-ID: <20220511115427.GU49344@nvidia.com>
Date:   Wed, 11 May 2022 08:54:27 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>, dmaengine@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, vkoul@...nel.org,
        robin.murphy@....com, will@...nel.org, Yi Liu <yi.l.liu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for
 attach_dev_pasid

On Tue, May 10, 2022 at 05:23:09PM -0700, Jacob Pan wrote:

> > > diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> > > index 5af24befc9f1..55845a8c4f4d 100644
> > > +++ b/include/linux/intel-iommu.h
> > > @@ -627,6 +627,7 @@ struct device_domain_info {
> > >  	struct intel_iommu *iommu; /* IOMMU used by this device */
> > >  	struct dmar_domain *domain; /* pointer to domain */
> > >  	struct pasid_table *pasid_table; /* pasid table */
> > > +	ioasid_t pasid; /* DMA request with PASID */  
> > 
> > And this seems wrong - the DMA API is not the only user of
> > attach_dev_pasid, so there should not be any global pasid for the
> > device.
> > 
> True but the attach_dev_pasid() op is domain type specific. i.e. DMA API
> has its own attach_dev_pasid which is different than sva domain
> attach_dev_pasid().

Huh? The intel driver shares the same ops between UNMANAGED and DMA -
and in general I do not think we should be putting special knowledge
about the DMA domains in the drivers. Drivers should continue to treat
them identically to UNMANAGED.

> device_domain_info is only used by DMA API.

Huh?
 
> > I suspect this should be a counter of # of pasid domains attached so
> > that the special flush logic triggers
> > 
> This field is only used for devTLB, so it is per domain-device. struct
> device_domain_info is allocated per device-domain as well. Sorry, I might
> have totally missed your point.

You can't store a single pasid in the driver like this, since the only
thing it does is trigger the flush logic just count how many pasids
are used by the device-domain and trigger pasid flush if any pasids
are attached

> > And rely on the core code to worry about assigning only one domain per
> > pasid - this should really be a 'set' function.
>
> Yes, in this set the core code (in dma-iommu.c) only assign one PASID per
> DMA domain type.
> 
> Are you suggesting the dma-iommu API should be called
> iommu_set_dma_pasid instead of iommu_attach_dma_pasid?

No that API is Ok - the driver ops API should be 'set' not attach/detach

Jason