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From: Paul Durrant <xadimgnik@gmail.com>
To: "\'Roman Shaposhnik\'" <roman@zededa.com>,
	"\'Roger Pau Monné\'" <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org,
	'Kevin Tian' <kevin.tian@intel.com>,
	'Jan Beulich' <jbeulich@suse.com>,
	'Andrew Cooper' <andrew.cooper3@citrix.com>
Subject: Re: [Xen-devel] PCIe IOMMU ACS support
Date: Fri, 27 Mar 2020 09:12:11 -0000
Message-ID: <000c01d60417$d3cacad0$7b606070$@xen.org> (raw)
In-Reply-To: <CAMmSBy_oX34t5388xYUxUE_jE56bpy=wKAfujZvR1-zaehDs3g@mail.gmail.com>

> -----Original Message-----
> From: Roman Shaposhnik <roman@zededa.com>
> Sent: 26 March 2020 22:03
> To: Roger Pau Monné <roger.pau@citrix.com>
> Cc: xen-devel@lists.xenproject.org; Jan Beulich <jbeulich@suse.com>; Paul Durrant <paul@xen.org>;
> Kevin Tian <kevin.tian@intel.com>; Andrew Cooper <andrew.cooper3@citrix.com>
> Subject: Re: [Xen-devel] PCIe IOMMU ACS support
> 
> On Wed, Mar 25, 2020 at 4:05 AM Roger Pau Monné <roger.pau@citrix.com> wrote:
> >
> > Adding the PCI and IOMMU maintainers.
> >
> > On Mon, Mar 23, 2020 at 01:55:01PM -0700, Roman Shaposhnik wrote:
> > > Hi!
> > >
> > > I was going through how Xen support PCIe IOMMU ACS and
> > > all I could find is this:
> > >     https://github.com/xen-project/xen/blob/master/xen/drivers/passthrough/pci.c#L608
> > > which looks to me as an attempt of enabling ACS opportunistically,
> > > but still proceeding forward even if it fails.
> >
> > That's correct AFAICT. Xen will try to enable some features, but will
> > proceed normally if ACS is not available, or if some of the features
> > are not implemented.
> >
> > Are you looking to ensure that all devices on the system have a
> > certain feature enabled?
> 
> My primary objective was to get some visibility into how Xen would
> prevent two PCIe devices behind a common bridge from doing p2p
> transactions (thus violating VM boundaries if those devices are
> assigned to different domains).
> 
> It looks like Xen simply trusts the hardware.
> 
> > Can you provide some more details about what you expect of ACS
> > handling?
> 
> I was actually surprised not to see IOMMU groups in the style of what
> VFIO https://www.kernel.org/doc/Documentation/vfio.txt
> 

I did write a doc some time ago to present the issues facing Xen w.r.t. IOMMU and device pass-through. Hopefully you can see it at https://docs.google.com/document/d/12-z6JD41J_oNrCg_c0yAxGWg5ADBQ8_bSiP_NH6Hqwo/edit?usp=sharing

  Paul



  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23 20:55 Roman Shaposhnik
2020-03-25 11:05 ` Roger Pau Monné
2020-03-26 22:03   ` Roman Shaposhnik
2020-03-27  9:12     ` Paul Durrant [this message]
2020-03-28  0:59       ` Roman Shaposhnik

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