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>,
	Jason Gunthorpe <jgg@nvidia.com>
Cc: Baolu Lu <baolu.lu@linux.intel.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 01:50:33 +0000	[thread overview]
Message-ID: <BN9PR11MB5276D8B0B6D51EA32A9CA50B8CDF9@BN9PR11MB5276.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220531134414.37a62c88@jacob-builder>

> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Sent: Wednesday, June 1, 2022 4:44 AM
> 
> Hi Jason,
> 
> On Tue, 31 May 2022 16:05:50 -0300, Jason Gunthorpe <jgg@nvidia.com>
> wrote:
> 
> > On Tue, May 31, 2022 at 10:29:55AM -0700, Jacob Pan wrote:
> >
> > > The reason why I store PASID at IOMMU domain is for IOTLB flush within
> > > the domain. Device driver is not aware of domain level IOTLB flush. We
> > > also have iova_cookie for each domain which essentially is for
> > > RIDPASID.
> >
> > You need to make the PASID stuff work generically.
> >
> > The domain needs to hold a list of all the places it needs to flush
> > and that list needs to be maintained during attach/detach.
> >
> > A single PASID on the domain is obviously never going to work
> > generically.
> >
> I agree, I did it this way really meant to be part of iommu_domain's
> iommu_dma_cookie, not meant to be global. But for the lack of common
> storage between identity domain and dma domain, I put it here as global.
> 
> Then should we also extract RIDPASID to become part of the generic API?
> i.e. set pasid, flush IOTLB etc. Right? RIDPASID is not in group's
> pasid_array today.
> 

RIDPASID is just an alias to RID in the PASID table (similar to pasid#0
on other platforms). it's reserved and not exposed outside the 
intel-iommu driver. So I don't think it should be managed via the
generic iommu API. But probably you can generalize it with other
pasids within intel-iommu driver if doing so can simplify the logic
there.