[Bug 1494602] [NEW] qemu-system-x86 nested virtualisation is broken on AMD system

[Andrew Spiers]

Public bug reported:

I am reporting this bug against qemu-system-x86=1:2.2+dfsg-5expubuntu9.3~cloud0 
in the Ubuntu cloud archive.                                                    


# lsb_release -rd                                                               
Description:    Ubuntu 14.04.3 LTS                                              
Release:        14.04                                                           
# apt-cache policy qemu-system-x86                                              
qemu-system-x86:                                                                
  Installed: 1:2.3+dfsg-5ubuntu4~cloud0                                         
  Candidate: 1:2.3+dfsg-5ubuntu4~cloud0                                         

What is happening:                                                              
Version 1:2.2+dfsg-5expubuntu9.3~cloud0 of qemu-system and qemu-system-x86_64   
seems to be dropping the svm (AMD nested virtualization) flag from virtual      
machines, despite it being specified in the CPU type. So nested virtualisation  
has stoppped working.                                                           

What I expect to happen:
svm CPU flag to be passed through to guests.           

Version 1:2.3+dfsg-5ubuntu4~cloud0 also drops the svm flag.

Version 2.0.0+dfsg-2ubuntu1.18 passes the CPU flag through fine.

This has been tested with libvirt-bin version 1.2.12-0ubuntu14. The processor   
is Version: AMD Opteron(TM) Processor 6238.                                     


# cat /sys/module/kvm_amd/parameters/nested                                     
1                                                                               
# modinfo kvm_amd | grep nested                                                 
parm:           nested:int                                                      


The qemu command line includes the following cpu argument::                     

    -cpu Opteron_G4,+perfctr_nb,+perfctr_core,+topoext,+nodeid_msr,+lwp,+wdt,+skinit,+ibs,+osvw,+cr8legacy,+extapic,+c
mp_legacy,+fxsr_opt,+mmxext,+osxsave,+monitor,+ht,+vme

** Affects: qemu (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1494602

Title:
  qemu-system-x86 nested virtualisation is broken on  AMD system

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