Re: [PATCH v6 01/21] backends/iommufd: Introduce the iommufd object

[Cédric Le Goater]

> > > > A similar issue with a fix submitted below, ccing related people.
> > > > https://lists.gnu.org/archive/html/qemu-devel/2023-11/msg02937.html
> > > > It looks the fix will not work for hotplug.
> > > >
> > > > Or below qemu cmdline may help:
> > > > "-cpu host,host-phys-bits-limit=39"
> > >
> > > don't you have the same issue with legacy VFIO code, you should?
> >
> > I tend to be lazy and use seabios for guests on the command line.
> > I do see the error with legacy VFIO and uefi.
> >
> > However, with the address space size work-around and iommufd, the
> > error is different, an EFAULT now. Some page pinning issue it seems.
>
> Yes, this reminds me of iommufd not supporting p2p mapping yet.

OK. Should we transform this error in a warning ? The code needs
at least a comment.

> So EFAULT is expected. Maybe I should add a comment in 
> docs/devel/vfio-iommufd.rst

Yes. It would be good to have a list of gaps and effects in the
documentation. See Jason's presentation at LPC.

  
https://lpc.events/event/17/contributions/1418/attachments/1297/2607/LPC2023_iommufd.pdf

Thanks,

C.