linux-kernel - Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID

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Message-ID: <20211002122542.GW964074@nvidia.com>
Date:   Sat, 2 Oct 2021 09:25:42 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "david@...son.dropbear.id.au" <david@...son.dropbear.id.au>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
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        "Raj, Ashok" <ashok.raj@...el.com>,
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        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: Re: [RFC 11/20] iommu/iommufd: Add IOMMU_IOASID_ALLOC/FREE

On Sat, Oct 02, 2021 at 02:21:38PM +1000, david@...son.dropbear.id.au wrote:

> > > No. qemu needs to supply *both* the 32-bit and 64-bit range to its
> > > guest, and therefore needs to request both from the host.
> > 
> > As I understood your remarks each IOAS can only be one of the formats
> > as they have a different PTE layout. So here I ment that qmeu needs to
> > be able to pick *for each IOAS* which of the two formats it is.
> 
> No.  Both windows are in the same IOAS.  A device could do DMA
> simultaneously to both windows.  

Sure, but that doesn't force us to model it as one IOAS in the
iommufd. A while back you were talking about using nesting and 3
IOAS's, right?

1, 2 or 3 IOAS's seems like a decision we can make.

PASID support will already require that a device can be multi-bound to
many IOAS's, couldn't PPC do the same with the windows?

Jason