7:38 p.m.
Hi Gianluca,
I'm also using the Pass-through Host CPU on my AMD cluster and I have never had such
behaviour.
This leads me to the Specte/Meltdown mitigations that are constantly affecting Intel's
CPUs.
As per https://access.redhat.com/solutions/4866021 you have to power off and then on the
VM or to find which mitigation is enforcing this flag and to disable it (if you think the
added security is not necessary).
Most probably avoiding the upgrade of the intel-ucode could save you the headaches - but
on a price (security is important and depends on the oVirt Usage).
Best Regards,
Strahil Nikolov
В понеделник, 2 март 2020 г., 13:12:06 ч. Гринуич+2, Gianluca Cecchi
<gianluca.cecchi(a)gmail.com> написа:
Hello,
I would like to share some problems that I'm finding on an environment based on RHV,
but could impact also oVirt based environments.
For my problems I'm working on an opened case to understand root cause.
I have Dell R730 hypervisors (with Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz cpu) and some
VMs configured for "customized" high performance.
In the sense that I configure VM as high performance type and then:
- I enable the graphical console (I remove the flag of headless Mode" in Console
section);
- In Host section I set for "Start Running On" Any Host in Cluster and allow
manual and automating migration;
- I also set HA in high availability section, accepting default values for leasing, resume
behaviour, ecc..
These settings however have the effect to leave enable the flag related to
"Pass-Through Host CPU" in Host section.
I noticed that with same Bios, ecc with kernel in 4.3.8 (that seems equal between oVirt
and RHV):
[g.cecchi@ov200 ~]$ uname -r
3.10.0-1062.12.1.el7.x86_64
[g.cecchi@ov200 ~]$
I have this cpu flag set: invpcid_single
Instead on the same host in 4.3.5 (eg kernel 3.10.0-1062.el7.x86_64) the flag is not set.
This creates problem during upgrade from 4.3.5 to 4.3.8 because initially I empty one host
and update it, but then I cannot live migrate back the VMs to update the other one, due to
the pass-through flag set, that requires exact set of flags.
So crosscheck on a test environment in case you have the "Pass-Through Host
CPU" set in Host section for any critical VM you cannot shutdown.
BTW: the flag is somehow tricky to remove if you set the VM as High Performance type; you
have to:
edit VM --> Host
Start Running On --> change to select a specific host among the available ones
Now you can remove the "Pass-Through Host CPU" flag --> remove it
Start Running On --> change again to "Any Host in Cluster"
Save
Now you can live migrate this "customized" High Performance VM
But the problem is that if the VM is running, you have to shutdown it to get the change in
effect.
HH,
Gianluca
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