[pve-devel] cpuflag: pcid needed in guest for good performance after meltdown

[Alexandre DERUMIER]

I think it's not exposed in current cpu model

it can be enabled with "+pcid"


I don't known what it's the best way to add it in proxmox.
We could do it with qemu version upgrade, but qemu 2.10 are not ready.

Maybe add new cpumodel with +pcid enabled ?
or add code to manage custom cpuflags and add a checkbox in cpu options ?



----- Mail original -----
De: "Stefan Priebe, Profihost AG" <s.priebe at profihost.ag>
À: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Lundi 8 Janvier 2018 21:34:57
Objet: [pve-devel] cpuflag: pcid needed in guest for good performance after meltdown

Hello, 

for meltdown mitigation and performance it's important to have the pcid 
flag passed down to the guest (f.e. 
https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU). 

My host shows the flag: 
# grep ' pcid ' /proc/cpuinfo | wc -l 
56 

But the guest does not: 
# grep pcid /proc/cpuinfo 
# 

Guest was started with: 
-cpu IvyBridge,+kvm_pv_unhalt,+kvm_pv_eoi,enforce,vendor=GenuineIntel 

Is this something missing in host kernel or in PVE? 

Greets, 
Stefan 
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