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Date:   Thu, 17 Jun 2021 12:42:31 +1000
From:   David Gibson <david@gibson.dropbear.id.au>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        David Woodhouse <dwmw2@infradead.org>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Alex Williamson (alex.williamson@redhat.com)" 
        <alex.williamson@redhat.com>, Jason Wang <jasowang@redhat.com>,
        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>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        Kirti Wankhede <kwankhede@nvidia.com>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal
Message-ID: <YMq2l7YId3cjmVKG@yekko>
References: <MWHPR11MB1886422D4839B372C6AB245F8C239@MWHPR11MB1886.namprd11.prod.outlook.com>
 <20210528173538.GA3816344@nvidia.com>
 <YLcl+zaK6Y0gB54a@yekko>
 <20210602161648.GY1002214@nvidia.com>
 <YLhlCINGPGob4Nld@yekko>
 <20210603115224.GQ1002214@nvidia.com>
 <YL6/bjHyuHJTn4Rd@yekko>
 <20210608190406.GN1002214@nvidia.com>
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On Tue, Jun 08, 2021 at 04:04:06PM -0300, Jason Gunthorpe wrote:
> On Tue, Jun 08, 2021 at 10:53:02AM +1000, David Gibson wrote:
> > On Thu, Jun 03, 2021 at 08:52:24AM -0300, Jason Gunthorpe wrote:
> > > On Thu, Jun 03, 2021 at 03:13:44PM +1000, David Gibson wrote:
> > >=20
> > > > > We can still consider it a single "address space" from the IOMMU
> > > > > perspective. What has happened is that the address table is not j=
ust a
> > > > > 64 bit IOVA, but an extended ~80 bit IOVA formed by "PASID, IOVA".
> > > >=20
> > > > True.  This does complexify how we represent what IOVA ranges are
> > > > valid, though.  I'll bet you most implementations don't actually
> > > > implement a full 64-bit IOVA, which means we effectively have a lar=
ge
> > > > number of windows from (0..max IOVA) for each valid pasid.  This ad=
ds
> > > > another reason I don't think my concept of IOVA windows is just a
> > > > power specific thing.
> > >=20
> > > Yes
> > >=20
> > > Things rapidly get into weird hardware specific stuff though, the
> > > request will be for things like:
> > >   "ARM PASID&IO page table format from SMMU IP block vXX"
> >=20
> > So, I'm happy enough for picking a user-managed pagetable format to
> > imply the set of valid IOVA ranges (though a query might be nice).
>=20
> I think a query is mandatory, and optionally asking for ranges seems
> generally useful as a HW property.
>=20
> The danger is things can get really tricky as the app can ask for
> ranges some HW needs but other HW can't provide.=20
>=20
> I would encourage a flow where "generic" apps like DPDK can somehow
> just ignore this, or at least be very, very simplified "I want around
> XX GB of IOVA space"
>=20
> dpdk type apps vs qemu apps are really quite different and we should
> be carefully that the needs of HW accelerated vIOMMU emulation do not
> trump the needs of simple universal control over a DMA map.

Agreed.

--=20
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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