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

From: Jason Gunthorpe <jgg@nvidia.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: iommu@lists.linux-foundation.org,
	LKML <linux-kernel@vger.kernel.org>,
	dmaengine@vger.kernel.org, Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Jean-Philippe Brucker <jean-philippe@linaro.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	vkoul@kernel.org, robin.murphy@arm.com, will@kernel.org,
	Yi Liu <yi.l.liu@intel.com>, Dave Jiang <dave.jiang@intel.com>,
	"Tian, Kevin" <kevin.tian@intel.com>,
	Raj Ashok <ashok.raj@intel.com>,
	Eric Auger <eric.auger@redhat.com>
Subject: Re: [PATCH v3 1/4] iommu/vt-d: Implement domain ops for attach_dev_pasid
Date: Wed, 11 May 2022 08:54:27 -0300	[thread overview]
Message-ID: <20220511115427.GU49344@nvidia.com> (raw)
In-Reply-To: <20220510172309.3c4e7512@jacob-builder>

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