RE: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

From: "Tian, Kevin" <kevin.tian@intel.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>,
	Baolu Lu <baolu.lu@linux.intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
	Joerg Roedel <joro@8bytes.org>,
	David Woodhouse <dwmw2@infradead.org>,
	"Jean-Philippe Brucker" <jean-philippe@linaro.com>,
	Christoph Hellwig <hch@infradead.org>,
	"vkoul@kernel.org" <vkoul@kernel.org>,
	"robin.murphy@arm.com" <robin.murphy@arm.com>,
	"will@kernel.org" <will@kernel.org>,
	"Liu, Yi L" <yi.l.liu@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	Eric Auger <eric.auger@redhat.com>
Subject: RE: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API
Date: Wed, 1 Jun 2022 01:43:25 +0000	[thread overview]
Message-ID: <BN9PR11MB5276A2B5E849C2153939934C8CDF9@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220531102955.6618b540@jacob-builder>

> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Wednesday, June 1, 2022 1:30 AM
> > >
> > > In both cases the pasid is stored in the attach data instead of the
> > > domain.
> > >
> So during IOTLB flush for the domain, do we loop through the attach data?

Yes and it's required.

> 
> > > DMA API pasid is no special from above except it needs to allow
> > > one device attached to the same domain twice (one with RID
> > > and the other with RID+PASID).
> > >
> > > for iommufd those operations are initiated by userspace via
> > > iommufd uAPI.
> >
> > My understanding is that device driver owns its PASID policy. If ENQCMD
> > is supported on the device, the PASIDs should be allocated through
> > ioasid_alloc(). Otherwise, the whole PASID pool is managed by the device
> > driver.
> >
> It seems the changes we want for this patchset are:
> 1. move ioasid_alloc() from the core to device (allocation scope will be
> based on whether ENQCMD is intended or not)

yes, and the driver can specify whether the allocation is system-wide
or per-device.

> 2. store pasid in the attach data
> 3. use the same iommufd api to attach/set pasid on its default domain

s/iommufd/iommu/