linux-kernel - RE: [RFC PATCH 2/7] iommu: Add share domain interface in iommu for spimdev

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Date:   Thu, 2 Aug 2018 04:39:37 +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 2/7] iommu: Add share domain interface in iommu for
 spimdev

> From: Kenneth Lee
> Sent: Thursday, August 2, 2018 12:16 PM
> 
> On Thu, Aug 02, 2018 at 03:17:03AM +0000, Tian, Kevin wrote:
> > > From: Kenneth Lee
> > > Sent: Wednesday, August 1, 2018 6:22 PM
> > >
> > > From: Kenneth Lee <liguozhu@...ilicon.com>
> > >
> > > This patch add sharing interface for a iommu_group. The new interface:
> > >
> > > 	iommu_group_share_domain()
> > > 	iommu_group_unshare_domain()
> > >
> > > can be used by some virtual iommu_group (such as iommu_group for
> > > spimdev)
> > > to share their parent's iommu_group.
> > >
> > > When the domain of the group is shared, it cannot be changed before
> > > unshared.  In the future, notification can be added if update is required.
> >
> > Is it necessary or just asking VFIO to use parent domain directly?
> >
> Even we add to VFIO, the iommu still need to be changed. We can move
> the type1
> part to VFIO if we have agreement in RFC stage.

We have similar consideration in IOMMU aware mdev series. Now
we are inclined to avoid faked entity within IOMMU layer - leave to
caller to figure out right physical entity for any IOMMU ops. That 
might be leveraged here too after we get a new version.

Thanks
Kevin