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[Launchpad Bug Tracker <1999814@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package nova - 2:21.2.4-0ubuntu2.13

---------------
nova (2:21.2.4-0ubuntu2.13) focal; urgency=medium

  * d/p/lp2024258-database-Archive-parent-and-child-rows-trees-one-at-.patch:
    Fix package install/autopkgtests (IndentationError in test_archive.py:172)
    (LP: #2024258)

nova (2:21.2.4-0ubuntu2.12) focal; urgency=medium

  [ Chengen Du ]
  * d/p/lp2024258-database-Archive-parent-and-child-rows-trees-one-at-.patch:
    Performance degradation archiving DB with large numbers of FK
    related records (LP: #2024258)

  [ Mauricio Faria de Oliveira ]
  * Extend the behavior of 'libvirt.cpu_model_extra_flags' for '[+-]flag'
    (backward compatible) to configure CPU flags as required or disabled.
    This is increasingly important for migration as hypervisors with the
    same processor but different stable kernel level might get different
    CPU flags (e.g., AMD EPYC Rome without 'xsaves' per AMD Erratum 1386,
    and PKRU/'xsave' changes), without CPU model updates in libvirt/qemu.
    (LP: #2048517)
    - d/p/lp2048517-1-libvirt-Dont-drop-disabled-CPU-flags-from-XML.patch
    - d/p/lp2048517-2-libvirt-Allow-disabling-CPU-flags.patch

  [ Rodrigo Barbieri ]
  * d/p/lp1999814.patch: Rework CPU comparison at startup and add ability
    to skip it. Addresses CascadeLake incompatibility with IceLake.
    (LP: #1999814)

 -- Mauricio Faria de Oliveira <mfo@xxxxxxxxxxxxx>  Thu, 02 Aug 2024
10:29:57 -0300

** Changed in: nova (Ubuntu Focal)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1999814

Title:
  [SRU] Allow for specifying common baseline CPU model with disabled
  feature

Status in OpenStack Compute (nova):
  Expired
Status in OpenStack Compute (nova) ussuri series:
  New
Status in OpenStack Compute (nova) victoria series:
  Won't Fix
Status in OpenStack Compute (nova) wallaby series:
  Won't Fix
Status in OpenStack Compute (nova) xena series:
  Won't Fix
Status in OpenStack Compute (nova) yoga series:
  New
Status in nova package in Ubuntu:
  Fix Released
Status in nova source package in Bionic:
  Won't Fix
Status in nova source package in Focal:
  Fix Released
Status in nova source package in Jammy:
  Fix Committed

Bug description:
  ******** SRU TEMPLATE AT THE BOTTOM *******

  Hello,

  This is very similar to pad.lv/1852437 (and the related blueprint at
  https://blueprints.launchpad.net/nova/+spec/allow-disabling-cpu-
  flags), but there is a very different and important nuance.

  A customer I'm working with has two classes of blades that they're
  trying to use.  Their existing ones are Cascade Lake-based; they are
  presently using the Cascadelake-Server-noTSX CPU model via
  libvirt.cpu_model in nova.conf.  Their new blades are Ice Lake-based,
  which is a newer processor, which typically would also be able to run
  based on the Cascade Lake feature set - except that these Ice Lake
  processors lack the MPX feature defined in the Cascadelake-Server-
  noTSX model.

  The result of this is evident when I try to start nova on the new
  blades with the Ice Lake CPUs.  Even if I specify the following in my
  nova.conf:

  [libvirt]
  cpu_mode = custom
  cpu_model = Cascadelake-Server-noTSX
  cpu_model_extra_flags = -mpx

  That is not enough to allow Nova to start; it fails in the libvirt
  driver in the _check_cpu_compatibility function:

  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service Traceback (most recent call last):
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/virt/libvirt/driver.py", line 771, in _check_cpu_compatibility
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     self._compare_cpu(cpu, self._get_cpu_info(), None)
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/virt/libvirt/driver.py", line 8817, in _compare_cpu
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     raise exception.InvalidCPUInfo(reason=m % {'ret': ret, 'u': u})
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service nova.exception.InvalidCPUInfo: Unacceptable CPU info: CPU doesn't have compatibility.
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service 0
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service Refer to http://libvirt.org/html/libvirt-libvirt-host.html#virCPUCompareResult
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service During handling of the above exception, another exception occurred:
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service Traceback (most recent call last):
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/oslo_service/service.py", line 810, in run_service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     service.start()
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/service.py", line 173, in start
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     self.manager.init_host()
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/compute/manager.py", line 1404, in init_host
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     self.driver.init_host(host=self.host)
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/virt/libvirt/driver.py", line 743, in init_host
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     self._check_cpu_compatibility()
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service   File "/usr/lib/python3/dist-packages/nova/virt/libvirt/driver.py", line 777, in _check_cpu_compatibility
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service     raise exception.InvalidCPUInfo(msg)
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service nova.exception.InvalidCPUInfo: Configured CPU model: Cascadelake-Server-noTSX is not compatible with host CPU. Please correct your config and try again. Unacceptable CPU info: CPU doesn't have compatibility.
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service 0
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service Refer to http://libvirt.org/html/libvirt-libvirt-host.html#virCPUCompareResult
  2022-12-15 17:20:59.562 1836708 ERROR oslo_service.service

  If I make a custom libvirt CPU map file which removes the "<feature
  name='mpx'/>" feature and specify that as the cpu_model instead, I am
  able to make Nova start - so it does indeed seem to specifically be
  that single feature which is blocking me.  However, editing the
  libvirt CPU mapping files is probably not the right way to fix this -
  hence why I'm filing this bug, for discussion of how to support cases
  like this.

  Currently the only "proper" way I'm aware of to work around this right
  now is to fall back to a Broadwell-based configuration which lacks the
  "mpx" feature to use as a common baseline, but that's a much older
  configuration than Cascade Lake and would mean missing out on all the
  other features which are common in both Cascade Lake and Ice Lake.  I
  would rather if there were a way to use the Cascade Lake settings but
  simply remove that "mpx" feature from use.

  ----

  Steps to reproduce
  ==================

  On an Ice Lake system lacking the MPX feature (e.g. /proc/cpuinfo
  reporting model of "Intel(R) Xeon(R) Gold 5318Y"), specify the
  following settings in nova.conf in libvirt settings:

  [libvirt]
  cpu_mode = custom
  cpu_model = Cascadelake-Server-noTSX
  cpu_model_extra_flags = -mpx

  Then try to start nova.

  Expected result
  ===============

  Nova should start since Cascadelake-Server-noTSX is a subset of
  Icelake-Server-noTSX, thus allowing the use of Cascadelake-Server-
  noTSX as a common baseline model for both Cascade Lake and Ice Lake
  servers.

  Actual result
  =============

  Nova refuses to start, claiming the specified CPU model is
  incompatible.  The "cpu_model_extra_flags = -mpx" config option does
  not help.

  Environment
  ===========

  Nova/OpenStack version: OpenStack Ussuri running on Ubuntu Focal.
  Specifically, nova packages are at version 2:21.2.4-0ubuntu2.

  Hypervisor: libvirt + KVM

  Other relevant notes
  ====================

  There are some other open related bugs.  The removal of the MPX
  feature in some Ice Lake processors has manifested in other ways as
  well.  These bugs are primarily in regards to the missing MPX feature
  breaking how Ice Lake processors are detected, so the nuance is
  somewhat different - however, they may be worth reviewing as well.

  * https://gitlab.com/libvirt/libvirt/-/issues/304: bug regarding the
  Icelake CPU maps in libvirt not working to detect certain Ice Lakes,
  instead detecting them as Broadwell-noTSX-IBRS according to "virsh
  capabilities" due to lacking the MPX feature.  (I've personally tested
  that removing the mpx feature from the associated CPU mapping files
  allows for detecting as Ice Lake, but that's not the correct way to
  fix this.)

  There is also an interesting comment on this bug at
  https://gitlab.com/libvirt/libvirt/-/issues/304#note_1065798706.  It
  basically implies that rather than looking at "virsh capabilities",
  "virsh domcapabilities" should be used instead as it seems to more
  correctly identify the CPU model even if there are disabled flags like
  MPX.

  * https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1978064:
  Launchpad-side bug regarding the above issue as encountered in Ubuntu.

  ===============
  SRU Description
  ===============

  [Impact]

  When using IceLake CPUs alongside CascadeLake CPUs, the Nova code does
  not start due to comparing CPU models. It fails before even comparing
  the flags. Unfortunately, IceLake CPUs are detected as having
  compatibility with Broadwell, not CascadeLake. Using Broadwell as a
  common denominator disables many modern features. The Libvirt upstream
  team will not add specific support to IceLake [1]. The fix [2] in Nova
  is to ignore CPU check (as a configurable workaround) as let libvirt
  handle the added/removed flags, which is assumed to work for this
  specific case.

  [Test case]

  Due to not having Icelake and Cascadelake CPUs in our usual lab for
  testing of this specific scenario, the test case for this could be
  either:

  1) run for this SRU is running the charmed-openstack-tester [1]
  against the environment containing the upgraded package (essentially
  as it would be in a point release SRU) and expect the test to pass.
  Test run evidence will be attached to LP.

  2) manually deploy nova and the necessary openstack services to get
  Nova to the code point of validating the issue in a single node. I
  already achieved this and was able to test the fix by hacking the node
  code to bypass the need of other services (conductor, keystone, mysql,
  etc) but for a proper validation a clean installation (without any
  hackery) is considered mandatory. In such case, the test case would
  be:

  a) Deploy nova and required services in an IceLake machine
  b) Make sure the nova.conf has:

  cpu_mode = custom
  cpu_models = Cascadelake-Server-noTSX
  cpu_model_extra_flags = -mpx

  c) Check /var/log/nova/nova-compute.log for a successful nova-compute
  service boot. It will not start properly without the fix, therefore
  presenting the error:

  2024-07-08 15:08:48.378 8399 CRITICAL nova [-] Unhandled error:
  nova.exception.InvalidCPUInfo: Configured CPU model: Cascadelake-
  Server-noTSX is not compatible with host CPU. Please correct your
  config and try again. Unacceptable CPU info: CPU doesn't have
  compatibility.

  d) Install package containing the fix and confirm the successful nova-
  compute service restart, not containing the error and containing this
  instead:

  2024-07-09 19:41:31.806 243487 DEBUG nova.virt.libvirt.driver [-] cpu compare xml: <cpu match="exact">
    <model>Cascadelake-Server-noTSX</model>
    <feature name="mpx" policy="disable"/>
  </cpu>

  
  [Regression Potential]

  There is 1 new behavior introduced and 1 changed. The behavior
  introduced is gated by a new config option that needs to be enabled,
  and when enabled, it skips running the code. The behavior changed is
  the one assumed by the default disabled value of the config option.
  The fact that the code being backported in Yoga-Ussuri is exactly the
  same as in currently Master (Caracal+), it means that no issues have
  been found with the code across 4 releases, giving some confidence
  that the code changed is unlikely to cause issues.

  [Other Info]

  [1] https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1978064
  [2] https://review.opendev.org/c/openstack/nova/+/871969

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