linux-kernel - RE: [RFC PATCH 3/7] vfio: add spimdev support

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Date:   Thu, 2 Aug 2018 04:24:22 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Kenneth Lee <liguozhu@...ilicon.com>
CC:     Kenneth Lee <nek.in.cn@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Hao Fang <fanghao11@...wei.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        Zaibo Xu <xuzaibo@...wei.com>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-accelerators@...ts.ozlabs.org" 
        <linux-accelerators@...ts.ozlabs.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>
Subject: RE: [RFC PATCH 3/7] vfio: add spimdev support

> From: Kenneth Lee [mailto:liguozhu@...ilicon.com]
> Sent: Thursday, August 2, 2018 11:47 AM
> 
> >
> > > From: Kenneth Lee
> > > Sent: Wednesday, August 1, 2018 6:22 PM
> > >
> > > From: Kenneth Lee <liguozhu@...ilicon.com>
> > >
> > > SPIMDEV is "Share Parent IOMMU Mdev". It is a vfio-mdev. But differ
> from
> > > the general vfio-mdev:
> > >
> > > 1. It shares its parent's IOMMU.
> > > 2. There is no hardware resource attached to the mdev is created. The
> > > hardware resource (A `queue') is allocated only when the mdev is
> > > opened.
> >
> > Alex has concern on doing so, as pointed out in:
> >
> > 	https://www.spinics.net/lists/kvm/msg172652.html
> >
> > resource allocation should be reserved at creation time.
> 
> Yes. That is why I keep telling that SPIMDEV is not for "VM", it is for "many
> processes", it is just an access point to the process. Not a device to VM. I
> hope
> Alex can accept it:)
> 

VFIO is just about assigning device resource to user space. It doesn't care
whether it's native processes or VM using the device so far. Along the direction
which you described, looks VFIO needs to support the configuration that
some mdevs are used for native process only, while others can be used
for both native and VM. I'm not sure whether there is a clean way to
enforce it...

Let's hear from Alex's thought.

Thanks
Kevin