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

From: "Tian, Kevin" <kevin.tian@intel.com>
To: Kenneth Lee <liguozhu@hisilicon.com>
Cc: Kenneth Lee <nek.in.cn@gmail.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S . Miller" <davem@davemloft.net>,
	Joerg Roedel <joro@8bytes.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	Hao Fang <fanghao11@huawei.com>,
	Zhou Wang <wangzhou1@hisilicon.com>,
	Zaibo Xu <xuzaibo@huawei.com>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-accelerators@lists.ozlabs.org" 
	<linux-accelerators@lists.ozlabs.org>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	"Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
	"linuxarm@huawei.com" <linuxarm@huawei.com>
Subject: RE: [RFC PATCH 2/7] iommu: Add share domain interface in iommu for spimdev
Date: Thu, 2 Aug 2018 04:39:37 +0000	[thread overview]
Message-ID: <AADFC41AFE54684AB9EE6CBC0274A5D19129107A@SHSMSX101.ccr.corp.intel.com> (raw)
In-Reply-To: <20180802041547.GM160746@Turing-Arch-b>

> 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@hisilicon.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