Re: [RFC v2] /dev/iommu uAPI proposal

From: David Gibson <david@gibson.dropbear.id.au>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: "Tian, Kevin" <kevin.tian@intel.com>,
	"Alex Williamson (alex.williamson@redhat.com)" 
	<alex.williamson@redhat.com>,
	Jean-Philippe Brucker <jean-philippe@linaro.org>,
	Jason Wang <jasowang@redhat.com>,
	"parav@mellanox.com" <parav@mellanox.com>,
	"Enrico Weigelt, metux IT consult" <lkml@metux.net>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Shenming Lu <lushenming@huawei.com>,
	Joerg Roedel <joro@8bytes.org>,
	Eric Auger <eric.auger@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	"Liu, Yi L" <yi.l.liu@intel.com>, "Wu, Hao" <hao.wu@intel.com>,
	"Jiang, Dave" <dave.jiang@intel.com>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>,
	Kirti Wankhede <kwankhede@nvidia.com>,
	Robin Murphy <robin.murphy@arm.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	David Woodhouse <dwmw2@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Lu Baolu <baolu.lu@linux.intel.com>
Subject: Re: [RFC v2] /dev/iommu uAPI proposal
Date: Fri, 6 Aug 2021 14:47:50 +1000	[thread overview]
Message-ID: <YQy+9mSSzban+t/X@yekko> (raw)
In-Reply-To: <20210804140447.GH1721383@nvidia.com>

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On Wed, Aug 04, 2021 at 11:04:47AM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 02, 2021 at 02:49:44AM +0000, Tian, Kevin wrote:
> 
> > Can you elaborate? IMO the user only cares about the label (device cookie 
> > plus optional vPASID) which is generated by itself when doing the attaching
> > call, and expects this virtual label being used in various spots (invalidation,
> > page fault, etc.). How the system labels the traffic (the physical RID or RID+
> > PASID) should be completely invisible to userspace.
> 
> I don't think that is true if the vIOMMU driver is also emulating
> PASID. Presumably the same is true for other PASID-like schemes.

Right.  The idea for an SVA capable vIOMMU in my scheme is that the
hypervisor would set up an IOAS of address type "PASID+address" with
the mappings made by the guest according to its vIOMMU semantics.
Then SVA capable devices would be plugged into that IOAS by using
"PASID+address" type endpoints from those devices.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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