Re: [Qemu-devel] [PATCH][RFC] IOMMU: Add Support to VFIO devices with vIOMMU present

[Michael S. Tsirkin]

On Mon, Mar 14, 2016 at 07:58:23PM +0100, Jan Kiszka wrote:
> On 2016-03-14 19:52, Marcel Apfelbaum wrote:
> > On 03/12/2016 06:13 PM, Aviv B.D. wrote:
> >> From: "Aviv B.D." <address@hidden <mailto:address@hidden>>
> >>
> >>   * Fix bug that prevent qemu from starting up when vIOMMU and VFIO
> >>      device are present.
> >>   * Advertise Cache Mode capability in iommu cap register.
> 
> For the final version: Please keep that feature optional, for the sake
> of emulation accuracy (no modern hw exposes it any more). Maybe turn it
> one once a vfio device is in the scope of the IOMMU?

That would be hard to implement: VFIO supports hotplug and there's no way to
change this on the fly.

I would say
        - make the feature an optional flag
        - deny adding a VFIO device if the flag is not set


> >>   * Register every VFIO device with IOMMU state.
> >>   * On page cache invalidation in vIOMMU, check if the domain belong to
> >>     VFIO device and mirror the guest requests to host.
> >>
> >> Not working (Yet!):
> >>   * Tested only with network interface card (ixgbevf) and
> >>      intel_iommu=strict in guest's kernel command line.
> >>   * Lock up under high load.
> >>   * Errors on guest poweroff.
> >>   * High relative latency compare to VFIO without IOMMU.
> > 
> > Adding (possibly) interested developers to the thread.
> 
> Thanks,
> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT RDA ITP SES-DE
> Corporate Competence Center Embedded Linux