need special CPU Flag


Well-Known Member
Sep 12, 2017

because of an Performance issue in SAP HANA System we need to add this CPU Flag to our VM:


i've added this in my vm.conf file but after that the VM had 64kvm CPU without any flags :(

cpu: Nehalem,flags=+md-clear;+pcid;+spec-ctrl;+ssbd

cpu: Nehalem,flags=+md-clear;+pcid;+spec-ctrl;+ssbd;+nonstop_tsc

all of our Proxmox Hosts have this FLAG (cat /proc/cpuinfo)
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 79
model name : Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz
stepping : 1
microcode : 0xb000033
cpu MHz : 2408.538
cache size : 20480 KB
physical id : 0
siblings : 16
core id : 0
cpu cores : 8
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 20
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb cat_l3 cdp_l3 invpcid_single pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdt_a rdseed adx smap intel_pt xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm ida arat pln pts flush_l1d
bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs
bogomips : 4195.12
clflush size : 64
cache_alignment : 64
address sizes : 46 bits physical, 48 bits virtual
power management:

proxmox package versions:
proxmox-ve: 5.4-2 (running kernel: 4.15.18-20-pve) pve-manager: 5.4-13 (running version: 5.4-13/aee6f0ec) pve-kernel-4.15: 5.4-8 pve-kernel-4.15.18-20-pve: 4.15.18-46 pve-kernel-4.15.18-12-pve: 4.15.18-36 ceph: 12.2.12-pve1 corosync: 2.4.4-pve1 criu: 2.11.1-1~bpo90 glusterfs-client: 3.8.8-1 ksm-control-daemon: 1.2-2 libjs-extjs: 6.0.1-2 libpve-access-control: 5.1-12 libpve-apiclient-perl: 2.0-5 libpve-common-perl: 5.0-54 libpve-guest-common-perl: 2.0-20 libpve-http-server-perl: 2.0-14 libpve-storage-perl: 5.0-44 libqb0: 1.0.3-1~bpo9 lvm2: 2.02.168-pve6 lxc-pve: 3.1.0-6 lxcfs: 3.0.3-pve1 novnc-pve: 1.0.0-3 proxmox-widget-toolkit: 1.0-28 pve-cluster: 5.0-38 pve-container: 2.0-40 pve-docs: 5.4-2 pve-edk2-firmware: 1.20190312-1 pve-firewall: 3.0-22 pve-firmware: 2.0-7 pve-ha-manager: 2.0-9 pve-i18n: 1.1-4 pve-libspice-server1: 0.14.1-2 pve-qemu-kvm: 3.0.1-4 pve-xtermjs: 3.12.0-1 qemu-server: 5.0-54 smartmontools: 6.5+svn4324-1 spiceterm: 3.0-5 vncterm: 1.5-3 zfsutils-linux: 0.7.13-pve1~bpo2

any suggestions?

thanks for your answer, but in dont know what i have todo..

like that?
args: -cpu Nehalem,+pcid,+spec-ctrl,+ssbd,+kvm_pv_unhalt,+kvm_pv_eoi,+nonstop_tsc,enforce,vendor=GenuineIntel
yes, something like that should work. if you ever change the CPU setting, you'd need to re-do that step (or upgrade to PVE 6 once the custom CPU models are available there ;))
ah, ok, it runs - but i have to chose "host" as cpu type.

thanks a lot :)
roughly related and I couldn't find this anywhere else so I figured I'll just leave it here for future reference:

I was only ever able to get the cpu flag/arg "PCLMUL" to activate by setting

args: -cpu qemu64,+sse4.2,+pclmulqdq

I needed both of these enabled in order for scylladb/scylla to work,
which in turn is a dependency of's docker setup.


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