Re: [PATCH] xen/pass-through: don't create needless register group

[Anthony PERARD]

On Fri, Jun 10, 2022 at 12:23:35PM -0400, Chuck Zmudzinski wrote:
> Currently we are creating a register group for the Intel IGD OpRegion
> for every device we pass through, but the XEN_PCI_INTEL_OPREGION
> register group is only valid for an Intel IGD. Add a check to make
> sure the device is an Intel IGD and a check that the administrator has
> enabled gfx_passthru in the xl domain configuration. Require both checks
> to be true before creating the register group. Use the existing
> is_igd_vga_passthrough() function to check for a graphics device from
> any vendor and that the administrator enabled gfx_passthru in the xl
> domain configuration, but further require that the vendor be Intel,
> because only Intel IGD devices have an Intel OpRegion. These are the
> same checks hvmloader and libxl do to determine if the Intel OpRegion
> needs to be mapped into the guest's memory.
> 
> Signed-off-by: Chuck Zmudzinski <brchuckz@aol.com>
> ---
>  hw/xen/xen_pt_config_init.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/hw/xen/xen_pt_config_init.c b/hw/xen/xen_pt_config_init.c
> index c5c4e943a8..ffd915654c 100644
> --- a/hw/xen/xen_pt_config_init.c
> +++ b/hw/xen/xen_pt_config_init.c
> @@ -2037,6 +2037,10 @@ void xen_pt_config_init(XenPCIPassthroughState *s, 
> Error **errp)
>           * therefore the size should be 0xff.
>           */

Could you move that comment? I think it would make more sense to comment
the "reg_grp_offset=XEN_PCI_INTEL_OPREGION" line now that the `if` block
also skip setting up the group on non-intel devices.

>          if (xen_pt_emu_reg_grps[i].grp_id == XEN_PCI_INTEL_OPREGION) {
> +            if (!is_igd_vga_passthrough(&s->real_device) ||
> +                s->real_device.vendor_id != PCI_VENDOR_ID_INTEL) {
> +                continue;
> +            }
>              reg_grp_offset = XEN_PCI_INTEL_OPREGION;
>          }

Thanks,

-- 
Anthony PERARD