KVM won't install with KVM capable CPU

Discussion in 'Linux, BSD and Other OS's' started by Fred, Nov 7, 2010.

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  1. Fred

    Fred Moderator

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    I'm running Debian Lenny on a system with an AMD Athlon II 240 CPU.

    I'm installing KVM on my Debian system (fully updated) following this walkthrough. After installing the Xen kernel and rebooting, I attempt to install kvm and get the following error:
    Code:
    slinky:/home/user# aptitude install kvm
    Reading package lists... Done
    Building dependency tree       
    Reading state information... Done
    Reading extended state information      
    Initializing package states... Done
    Reading task descriptions... Done  
    The following NEW packages will be installed:
      kvm 
    0 packages upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
    Need to get 1111kB of archives. After unpacking 3121kB will be used.
    Writing extended state information... Done
    Get:1 http://ftp.us.debian.org lenny/main kvm 72+dfsg-5~lenny5 [1111kB]
    Fetched 1111kB in 1s (726kB/s)
    Selecting previously deselected package kvm.
    (Reading database ... 29584 files and directories currently installed.)
    Unpacking kvm (from .../kvm_72+dfsg-5~lenny5_amd64.deb) ...
    Processing triggers for man-db ...
    Setting up kvm (72+dfsg-5~lenny5) ...
    Your system does not have the CPU extensions required to use KVM. Not doing anything. failed!
    Reading package lists... Done             
    Building dependency tree       
    Reading state information... Done
    Reading extended state information      
    Initializing package states... Done
    Writing extended state information... Done
    Reading task descriptions... Done         
    
    slinky:/home/user# egrep '(vmx|svm)' --color=always /proc/cpuinfo
    
    But when I run
    Code:
    egrep '(vmx|svm)' --color=always /proc/cpuinfo
    the above code in the normal kernel (the one that installed with the OS), I get the proper CPU extensions.

    Everything I can find says my CPU supports KVM and obviously Debian does as well, but once I boot into a Xen kernel, I can't install KVM. Anybody know what the deal is?
     
  2. Anti-Trend

    Anti-Trend Nonconformist Geek Staff Member

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    Are you running a 32-bit or 64-bit kernel in Xen?
     
  3. Fred

    Fred Moderator

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    64-bit.
     
  4. Anti-Trend

    Anti-Trend Nonconformist Geek Staff Member

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    Hmmm, does /dev/kvm already exist?
     
  5. Fred

    Fred Moderator

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    Code:
    slinky:/home/user# ls /dev/kvm
    ls: cannot access /dev/kvm: No such file or directory
    Nope.

    *EDIT*
    According to this site, "You'll never see (vmx|svm) in /proc/cpuinfo if you're currently running in in a dom0 or domU.
    The Xen hypervisor suppresses these flags in order to prevent hijacking. " so it's going to be impossible to install kvm while booted in a xen kernel right?
     
  6. Fred

    Fred Moderator

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    If I reboot to a normal kernel I'm able to install kvm no problem. But once I boot back to the normal kernel, the module doesn't load and I can't reinstall it as it fails with the same error.
     
  7. Anti-Trend

    Anti-Trend Nonconformist Geek Staff Member

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    Yup, this sounds like a chicken/egg bug between Deb's implementation of KVM and Xen. Of course, in Xen you're not directly using KVM anyway, but merely its kernel hooks to accelerate QEMU for HVM domains. You can get similar results in Lenny by using the kqemu module, which doesn't require any specific CPU flags to install.
     
  8. Fred

    Fred Moderator

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    :-/ I guess I'll just go ahead and use the kqemu module. I was hoping to experiment with KVM some since I used kqemu in the past. Thanks AT.
     
  9. Anti-Trend

    Anti-Trend Nonconformist Geek Staff Member

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    Well, Xen uses QEMU to run HVM domains, not KVM, so there really isn't much of a practical difference. In a Xen environment, KVM (or kqemu) is simply used to accelerate HVM domains. PV domains aren't affected either way, and that's really where Xen shines.
     
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