Re: [PATCH v5 07/11] xen/domctl: Introduce XEN_DOMCTL_CDF_vpci flag

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 11 Oct 2021, Roger Pau Monné wrote:
> On Wed, Oct 06, 2021 at 06:40:33PM +0100, Rahul Singh wrote:
> > Introduce XEN_DOMCTL_CDF_vpci flag to enable VPCI support in XEN.
> > Reject the use of this new flag for x86 as VPCI is not supported for
> > DOMU guests for x86.
> 
> I don't like this approach, XEN_DOMCTL_CDF_vpci should be set for x86
> PVH dom0, like we do for any other CDF flags when Xen builds dom0.
> 
> Things like PVH vs PV get translated into CDF flags by create_dom0,
> and processed normally by the sanitise_domain_config logic, vPCI
> should be handled that way.
> 
> Do you think you could see about fixing this?

Andrew suggested to use XEN_SYSCTL_PHYSCAP_vpci to check whether we can
set XEN_DOMCTL_CDF_vpci in libxl and it looks like we have consensus on
this approach. [1][2]

So it makes sense that XEN_DOMCTL_CDF_vpci is only set when
XEN_SYSCTL_PHYSCAP_vpci is also set, i.e. XEN_SYSCTL_PHYSCAP_vpci ==
XEN_DOMCTL_CDF_vpci.

>From [2], XEN_SYSCTL_PHYSCAP_vpci is not going to be set on x86, so then
XEN_DOMCTL_CDF_vpci should also be left unset?

If you think XEN_DOMCTL_CDF_vpci should be set for x86 PVH Dom0, then
XEN_SYSCTL_PHYSCAP_vpci should also be set for x86 PVH Dom0.


[1] https://marc.info/?l=xen-devel&m=163372953907637
[2] https://marc.info/?l=xen-devel&m=163395821428850