Re: [PATCH v2] tools/libxl: don't allow IOMMU usage with PoD

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Feb 15, 2022 at 03:08:21PM +0000, Anthony PERARD wrote:
> On Thu, Feb 03, 2022 at 03:32:11PM +0100, Roger Pau Monne wrote:
> >      if (d_config->c_info.type != LIBXL_DOMAIN_TYPE_PV &&
> > -        d_config->num_pcidevs && pod_enabled) {
> > +        d_config->c_info.passthrough != LIBXL_PASSTHROUGH_DISABLED &&
> > +        pod_enabled) {
> >          ret = ERROR_INVAL;
> > -        LOGD(ERROR, domid,
> > -             "PCI device assignment for HVM guest failed due to PoD 
> > enabled");
> > +        LOGD(ERROR, domid, "IOMMU not supported together with PoD");
> 
> I'm not sure that this new error message is going to be good enough to
> point out configuration issue for the guest.
> 
> One is going to set 'pci=["foo"]' or 'dtdev=["bar"]', which will enable
> passthrough. Then they may get en error about IOMMU or PoD.
> Should we maybe write something like this instead?
> 
>    "IOMMU or device passthrough not supported together with PoD"

The "or" seems weird to me: IOMMU is mandatory for device passthrough.
Maybe:

"IOMMU required for device passthrough but not support together with PoD"

Would that be OK?

Thanks, Roger.