> -----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
