Re: [Xen-devel] [PATCH] libxl: change default QEMU machine to pc-i440fx-1.6

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 23 May 2014, Fabio Fantoni wrote:
> Il 23/05/2014 18:07, Stefano Stabellini ha scritto:
> > Choose pc-i440fx-1.6 instead of pc for HVM guests, so that we know for
> > sure what is the machine that we are emulating.
> > 
> > Use pc-i440fx-1.6 regardless of the xen_platform_pci option. Add the
> > xen-platform device if requested. Choose slot 2 for the xen-platform
> > device for compatibility with current installations. In case of Intel
> > graphic passthrough, slot 2 might be needed by the grafic card. However
> > now that we can specify the slot explicitly, it is easy to change the
> > position of the xen-platform device on the PCI bus if graphic
> > passthrough is enabled.
> > 
> > Move the machine options earlier, before any other emulated devices
> > options. Otherwise the selected PCI slot for the xen-platform device is
> > not available in QEMU.
> > 
> > Specify PIIX4_PM.acpi-pci-hotplug-with-bridge-support=off, because
> > differently from xenfv, the other QEMU machines do not have that option
> > off by default.
> > 
> > This patch does not change the emulated environment in the guest.
> > 
> > Refer to this thread: http://marc.info/?l=xen-devel&m=140023775929625&w=2
> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> > 
> > diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
> > index 8abed7b..fef684f 100644
> > --- a/tools/libxl/libxl_dm.c
> > +++ b/tools/libxl/libxl_dm.c
> > @@ -476,6 +476,29 @@ static char **
> > libxl__build_device_model_args_new(libxl__gc *gc,
> >           flexarray_vappend(dm_args, "-k", keymap, NULL);
> >       }
> >   +    flexarray_append(dm_args, "-machine");
> > +    switch (b_info->type) {
> > +    case LIBXL_DOMAIN_TYPE_PV:
> > +        flexarray_append(dm_args, "xenpv");
> > +        for (i = 0; b_info->extra_pv && b_info->extra_pv[i] != NULL; i++)
> > +            flexarray_append(dm_args, b_info->extra_pv[i]);
> > +        break;
> > +    case LIBXL_DOMAIN_TYPE_HVM:
> > +        flexarray_append(dm_args, "pc-i440fx-1.6,accel=xen");
> > +        flexarray_append(dm_args, "-global");
> > +        flexarray_append(dm_args,
> > "PIIX4_PM.acpi-pci-hotplug-with-bridge-support=off");
> 
> I think is good add a comment for remember to remove this workaround when pc
> >=2.1 will be the default since qemu 2.1 will fix it.
> https://lists.gnu.org/archive/html/qemu-devel/2014-05/msg04789.html

The workaround is not actually harmful, it doesn't need to be removed
when pc >= 2.1 in QEMU.


> > +        if (libxl_defbool_val(b_info->u.hvm.xen_platform_pci)) {
> > +            flexarray_append(dm_args, "-device");
> > +            flexarray_append(dm_args, "xen-platform,addr=0x2");
> 
> The fixed pci address to 0x2 probably is a problem with intel gpu passthrough:
> http://lists.gnu.org/archive/html/qemu-devel/2014-05/msg03726.html

Right, however we cannot really change the default position of the
xen-platform device on the PCI bus, otherwise we'll end up changing the
emulated environment for all the VMs out there.

I'll leave it to Tiejun to move xen-platform to another slot when
graphic passthrough is enabled.

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