On Fri, Mar 27, 2020 at 2:12 AM Paul Durrant <xadimg...@gmail.com> wrote: > > > -----Original Message----- > > From: Roman Shaposhnik <ro...@zededa.com> > > Sent: 26 March 2020 22:03 > > To: Roger Pau Monné <roger....@citrix.com> > > Cc: xen-devel@lists.xenproject.org; Jan Beulich <jbeul...@suse.com>; Paul > > Durrant <p...@xen.org>; > > Kevin Tian <kevin.t...@intel.com>; Andrew Cooper <andrew.coop...@citrix.com> > > Subject: Re: [Xen-devel] PCIe IOMMU ACS support > > > > On Wed, Mar 25, 2020 at 4:05 AM Roger Pau Monné <roger....@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, this is *exactly* what I was asking about -- thanks for the link. I guess the only question I have left is whether there was any follow up regarding what you sketched out in the "IOMMU drivers" section? Thanks, Roman.
