linux-kernel - Re: [RFC PATCH 03/10] iommu/vt-d: Allocate groups for mediated devices

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Message-ID: <20180724135101.58e81678@t450s.home>
Date:   Tue, 24 Jul 2018 13:51:01 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     Lu Baolu <baolu.lu@...ux.intel.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>
Subject: Re: [RFC PATCH 03/10] iommu/vt-d: Allocate groups for mediated
 devices

On Tue, 24 Jul 2018 12:30:35 +0100
Jean-Philippe Brucker <jean-philippe.brucker@....com> wrote:

> Hi Baolu,
> 
> On 24/07/18 03:22, Lu Baolu wrote:
> > Hi,
> > 
> > On 07/23/2018 12:44 PM, Liu, Yi L wrote:  
> >>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
> >>> Sent: Sunday, July 22, 2018 2:09 PM
> >>>
> >>> With the Intel IOMMU supporting PASID granularity isolation and protection, a
> >>> mediated device could be isolated and protected by an IOMMU unit. We need to
> >>> allocate a new group instead of a PCI group.  
> >> Existing vfio mdev framework also allocates an iommu group for mediate device.
> >>
> >> mdev_probe()
> >>   |_ mdev_attach_iommu()
> >>        |_ iommu_group_alloc()  
> > 
> > When external components ask iommu to allocate a group for a device,
> > it will call pci_device_group in Intel IOMMU driver's @device_group
> > callback. In another word, current Intel IOMMU driver doesn't aware
> > the mediated device and treat all devices as PCI ones. This patch
> > extends the @device_group call back to make it aware of a mediated
> > device.  
> 
> I agree that allocating two groups for an mdev seems strange, and in my
> opinion we shouldn't export the notion of mdev to IOMMU drivers.

Yep, I was just thinking the same thing.  This is too highly integrated
into VT-d and too narrowly focused on PASID being the only way that an
mdev could make use of the IOMMU.  Thanks,

Alex