linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Date:   Fri, 4 Jun 2021 09:33:52 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     David Gibson <david@...son.dropbear.id.au>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Fri, Jun 04, 2021 at 06:08:28AM +0000, Tian, Kevin wrote:

> In Qemu case the problem is that it doesn't know the list of devices
> that will be attached to an IOASID when it's created. This is a guest-
> side knowledge which is conveyed one device at a time to Qemu 
> though vIOMMU.

At least for the guest side it is alot simpler because the vIOMMU
being emulated will define nearly everything. 

qemu will just have to ask the kernel for whatever it is the guest is
doing. If the kernel can't do it then qemu has to SW emulate.

The no-snoop block may be the only thing that is under qemu's control
because it is transparent to the guest.

This will probably become clearer as people start to define what the
get_info should return.

Jason