From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: [vfio-users] [PATCH v3 00/11] igd passthrough
	chipset tweaks
Date: Tue, 02 Feb 2016 08:43:29 +0100
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To: Alex Williamson <alex.williamson@redhat.com>
Cc: igvt-g@ml01.01.org, xen-devel@lists.xensource.com, Eduardo Habkost <ehabkost@redhat.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, qemu-devel@nongnu.org, Cao jin <caoj.fnst@cn.fujitsu.com>, vfio-users@redhat.com
List-Id: xen-devel@lists.xenproject.org

  Hi,

> +realloc:
> +    opregion =3D 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.
>=20
> Ah, so here is where we'd clobber data in firmware.  I currently do
> this in vfio's pci config write in QEMU:
>=20
>         orig =3D pci_get_long(pdev->config + IGD_OPREGION);
>         pci_default_write_config(pdev, addr, val, len);
>         cur =3D pci_get_long(pdev->config + IGD_OPREGION);
>=20
>         if (cur !=3D orig) {
>             if (orig) {
>                 memory_region_del_subregion(get_system_memory(),
>                                             vdev->igd_opregion->mem);
>             }
>=20
>             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