Re: [PATCH v5 5/5] qemu: add default_cpu_deprecated_features configuration option

On 7/1/25 10:46, Daniel P. Berrangé via Devel wrote: > On Sun, Jun 29, 2025 at 11:19:30PM -0400, Collin Walling wrote: > > From: Boris Fiuczynski <fiuczy(a)linux.ibm.com&gt; > > > > Allow to define the default for deprecated_features when the attribute > > is not set in the cpu defintion of a domain XML. If these features are > > still desired, they may be reenabled via the deprecated_features='on' > > attribute. > > > > Some existing tests utilize this updated behavior, so update the CPU > > features on the corresponding args files. > > > > Signed-off-by: Boris Fiuczynski <fiuczy(a)linux.ibm.com&gt; > > Signed-off-by: Collin Walling <walling(a)linux.ibm.com&gt; > > --- > > src/qemu/libvirtd_qemu.aug | 3 ++ > > src/qemu/qemu.conf.in | 14 ++++++++ > > src/qemu/qemu_conf.c | 33 +++++++++++++++++++ > > src/qemu/qemu_conf.h | 12 +++++++ > > src/qemu/qemu_process.c | 26 ++++++++++++++- > > src/qemu/test_libvirtd_qemu.aug.in | 1 + > > ...deprecated-features-none.s390x-latest.args | 2 +- > > ...default-video-type-s390x.s390x-latest.args | 2 +- > > ...vfio-zpci-ccw-memballoon.s390x-latest.args | 2 +- > > .../launch-security-s390-pv.s390x-latest.args | 2 +- > > ...t-cpu-kvm-ccw-virtio-4.2.s390x-latest.args | 2 +- > > .../s390-defaultconsole.s390x-latest.args | 2 +- > > .../s390-panic.s390x-latest.args | 2 +- > > 13 files changed, 95 insertions(+), 8 deletions(-) > > > > diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug > > index e1e479d72c..2b674d258d 100644 > > --- a/src/qemu/libvirtd_qemu.aug > > +++ b/src/qemu/libvirtd_qemu.aug > > @@ -160,6 +160,8 @@ module Libvirtd_qemu = > > let filesystem_entry = str_array_entry "shared_filesystems" > > + let default_cpu_deprecated_features = str_entry "default_cpu_deprecated_features" > > + > > (* Entries that used to exist in the config which are now > > * deleted. We keep on parsing them so we don't break > > * ability to parse old configs after upgrade > > @@ -192,6 +194,7 @@ module Libvirtd_qemu = > > | capability_filters_entry > > | storage_entry > > | filesystem_entry > > + | default_cpu_deprecated_features > > | obsolete_entry > > let comment = [ label "#comment" . del /#[ \t]*/ "# " . store /([^ \t\n][^\n]*)?/ . del /\n/ "\n" ] > > diff --git a/src/qemu/qemu.conf.in b/src/qemu/qemu.conf.in > > index 221bfa8095..368d929f78 100644 > > --- a/src/qemu/qemu.conf.in > > +++ b/src/qemu/qemu.conf.in > > @@ -1100,3 +1100,17 @@ > > # "/path/to/nvram", > > # "/path/to/swtpm" > > #] > > + > > +# If QEMU provides a list of deprecated CPU features it is possible to use > > +# this list for removal of deprecated CPU features during CPU model expansion. > > +# The deprecated_features XML attribute on the XML CPU element in the domain > > +# XML can be used to turn deprecated CPU features 'off' or 'on'. Using the > > +# option default_cpu_deprecated_features allows to define the default behavior > > +# when the attribute deprecated_features is not provided in the domain XML. > > +# > > +# Possible options are: > > +# "off" - (default) deprecated features are removed during CPU model expansion > > +# "on" - deprecated features remain required in the expanded CPU model > > +# "none" - no deprecated_features attribute is added to expanded CPU model > > +# > > +#default_cpu_deprecated_features = "off" > > Having a host level config parameter change the guest ABI seems like a > bad idea to me. IMHO mgmt apps should be updated to use the XML to request > deprecated features are turned off by default. it has been some time but the idea originally is yours. https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/message/M...

The config parameter gives customers that still make use of the deprecated features in most of there guests the option to bail out of the default switch without having to edit all there guests. Of course they will give up a migrate to a CPU generation which no longer supports the cpu features to work out of the box. The default is switched in this patch to use deprecated_features = "off" which disables all deprecated cpu features without using of the config parameter.