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

[Fabio Fantoni <fabio.fantoni@m2r.biz>]

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Il 28/05/2014 18:53, Fabio Fantoni ha scritto:
> 2014-05-28 18:41 GMT+02:00 Stefano Stabellini 
> <stefano.stabellini@eu.citrix.com 
> <mailto:stefano.stabellini@eu.citrix.com>>:
>
>     On Wed, 28 May 2014, Stefano Stabellini wrote:
>     > On Wed, 28 May 2014, Fabio Fantoni wrote:
>     > > Il 26/05/2014 10:00, Fabio Fantoni ha scritto:
>     > > > 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@eu.citrix.com
>     <mailto:stefano.stabellini@eu.citrix.com>>
>     > > > > > >
>     > > > > > > 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.
>     > > >
>     > >
>     > > I found another case of problem with xen-platform's fixed pci
>     slot.
>     > > I tested this patch and I saw that qemu not start also in
>     other cases, for
>     > > example the domU of my test:
>     > > > qemu-system-i386: -device xen-platform,addr=0x2: PCI: slot 2
>     function 0 not
>     > > > available for xen-platform, in use by intel-hda
>     > > > qemu-system-i386: -device xen-platform,addr=0x2: Device
>     initialization
>     > > > failed.
>     > > > qemu-system-i386: -device xen-platform,addr=0x2: Device
>     'xen-platform' could
>     > > > not be initialized
>     > >
>     > > The domU's xl cfg:
>     > > > name='W7'
>     > > > builder="hvm"
>     > > > #device_model_override="/usr/lib/xen/bin/qemu-gdb"
>     > > > #device_model_override="/usr/bin/qemu-system-x86_64"
>     > > > #bios="ovmf"
>     > > > memory=2048
>     > > > vcpus=2
>     > > > #nestedhvm=1
>     > > > #vif=['model=e1000,bridge=xenbr0']
>     > > > vif=['bridge=xenbr0,mac=00:16:3e:42:ae:8f']
>     > > >
>     disk=['/mnt/vm/disks/W7.disk1.xm,raw,hda,rw',',raw,hdb,ro,cdrom']
>     > > > boot='dc'
>     > > > device_model_version="qemu-xen"
>     > > > viridian=1
>     > > > vnc=0
>     > > > keymap="it"
>     > > > on_crash="destroy"
>     > > > vga="qxl"
>     > > > #videoram=64
>     > > > spice=1
>     > > > spicehost='0.0.0.0'
>     > > > spiceport=6002
>     > > > spicedisable_ticketing=1
>     > > > spicevdagent=1
>     > > > spice_clipboard_sharing=0
>     > > > spice_image_compression="off"
>     > > > spice_streaming_video="filter"
>     > > > spiceusbredirection=4
>     > > > soundhw="hda"
>     >
>     > >From the error message, it looks like soundhw is the option that
>     > conflicts with xen-platform,addr=0x2.
>     >
>     >
>     > > > localtime=1
>     > > > usbversion=2
>     > >
>     > > Probably there are also other cases that can create a problem with
>     > > xen-platform fixed address, FWIK now new usb controller (with
>     usbversion) is
>     > > the only other with fixed pci address in libxl, all other
>     emulated qemu
>     > > components not.
>     > > And call it before in qemu binary starts notaffect the pci
>     slot order because
>     > > the xen-platform is already before audio.
>     >
>     > Actually it looks like that by passing -device xen-platform
>     before the
>     > other options, it already tries to assign slot 2 if possible. I
>     don't
>     > need to specify addr=0x2. That seems to be the best course of
>     action.
>
>     However it would still place xen-platform at slot 3 instead of
>     slot 2 if
>     soundhw is specified. It seems to me that there is not a perfect
>     solution to this problem.  We can either:
>
>     - Switch to -machine pc-i440fx-1.6 by default and use consistently the
>     same -machine option no matter the value of xen_platform_pci.
>     Nice, but
>     we break compatibility with existing guests if soundhw is specified.
>
>     - Switch to -machine pc-i440fx-1.6 only when xen_platform_pci=0 is
>     specified and keep xenfv if xen_platform_pci=1. We still break
>     compatibility when soundhw is specified together with
>     xen_platform_pci=0.
>
>
> FWIK removing the xen-platform's fixed pci slot will keep 
> compatibility in any cases, assigning slots as it did before.
> I'll try tomorrow.
> Otherwise I think there would be problems in other cases, not only 
> audio case.
> Perhaps even with save/restore/migrate.
>

Removing xen-platform's fixed pci slot works, I not found any case with 
problem for now.
The only problem probably will be only intel graphic passthrough (not 
tested), same with fixed pci slot of starting patch.


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