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

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 25/05/2014 16:14, Stefano Stabellini ha scritto:
> 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");
I think that a note in README should be added: qemu >=1.6.1 is required 
for hvm domUs.
About the other xl parameter to be added I think that should be:
qemu_machine_type="i440fx"|"q35" (when also q35 will be supported on xen)
qemu_machine_version="x.y" to specify the machine version, useful for 
debug/testing and other some cases.
> > > +        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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