Re: [Qemu-devel] [vfio-users] [PATCH v3 00/11] igd passthrough chipset tweaks

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> +realloc:
> +    opregion = malloc_high(size * 1024);

memalign_high(PAGE_SIZE, size * 1024);

> > I'd have qemu copy the data on 0xfc write then, so things continue to
> > work without updating seabios.  So, the firmware has to allocate space,
> > reserve it etc.,  and programming the 0xfc register.  Qemu has to make
> > sure the opregion appears at the address written by the firmware, by
> > whatever method it prefers.
> 
> Ah, so here is where we'd clobber data in firmware.  I currently do
> this in vfio's pci config write in QEMU:
> 
>         orig = pci_get_long(pdev->config + IGD_OPREGION);
>         pci_default_write_config(pdev, addr, val, len);
>         cur = pci_get_long(pdev->config + IGD_OPREGION);
> 
>         if (cur != orig) {
>             if (orig) {
>                 memory_region_del_subregion(get_system_memory(),
>                                             vdev->igd_opregion->mem);
>             }
> 
>             if (cur) {
>                 memory_region_add_subregion(get_system_memory(),
>                                             cur, vdev->igd_opregion->mem);
>             }
>         }

Ok, so we avoid the clobber and qemu sill has the choice to implement
the opregion in different ways, by simply changing how
vdev->igd_opregion->mem is backed.  Good.

cheers,
  Gerd