Re: PCI Passthrough

Laine Stump <laine@xxxxxxxxx> · Tue, 21 Jan 2014 15:47:25 +0200



    On 01/19/2014 04:13 AM, The PowerTool
      wrote:

    
      I'm trying to pass-through my VGA card to a guest
        session.

        
        I found: 
        http://www.linux-kvm.org/page/How_to_assign_devices_with_VT-d_in_KVM
        - which is very frustrating because there's no date on the
        documentation.  I suspect it's old.  It does clearly say that
        you must have VT-d support for pci pass-through.  It then goes
        on to say "Some work towards allowing this ["software
        pass-through"] were done, but the code never made it into KVM". 
        If this is old is there now support for PCI pass-through on
        hardware that doesn't support VT-d?

      
    No. Kvm does not support PCI passthrough in any form on hardware
    that doesn't support VT-d; it is too unsafe. Apparently Xen supports
    it in PV mode, but this too is completely unsafe.

    
    As far as passing through a VGA device. This is the complete
    bleeding edge of PCI device passthrough, and is difficult to the
    point of being practically impossible in many/most cases, especially
    for older VGA cards that weren't written with that idea in mind.
    Here is the page I was pointed to by Alex Williamson, who may have
    the most information on this topic:

    
       https://bbs.archlinux.org/viewtopic.php?id=162768

    
        I have a HP p7-1456c which has:

        
        Intel Core i5-3330 Processor (VT-x=yes, VT-d=yes)

        http://ark.intel.com/products/65509/Intel-Core-i5-3330-Processor-6M-Cache-up-to-3_20-GHz

        
        on a MB: H-Joshua-H61-UATX (with specs that say *nothing* about
        virtualization)

        http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c03135925#N98

        
        and the H-Joshua-H61-UATX uses the Intel H61 Express Chipset
        (VT-d=No)

        http://ark.intel.com/products/52806/Intel-BD82H61-PCH?q=intel%20h61%20express%20chipset

        
        On the KVM how to assign devices page it provides a way to
        verify IOMMU support on Intel:

        
        ]# dmesg | grep -e DMAR -e IOMMU

        [    0.000000] ACPI: DMAR 00000000d8d29460 000B0 (v01 HPQOEM
        SLIC-CPC 00000001 INTL 00000001)

        [    0.023074] dmar: IOMMU 0: reg_base_addr fed90000 ver 1:0 cap
        c0000020e60262 ecap f0101a

        [    0.023078] dmar: IOMMU 1: reg_base_addr fed91000 ver 1:0 cap
        c9008020660262 ecap f0105a

        [    0.023151] IOAPIC id 2 under DRHD base  0xfed91000 IOMMU 1

        
        Does this mean I do have VT-d/IOMMU support???

      
    I was told to look for this line on Intel hosts:

    
     "PCI-DMA: Intel(R) Virtualization Technology for Directed I/O"

    
        I attempted to follow the basic instructions to pass through my
        VGA card:

      
    *very* unlikely to work, unless you're lucky enough to have one of
    the few cards that has had their "quirks" worked out.

    
        ]$ lspci -nn | grep VGA

        00:02.0 VGA compatible controller [0300]: Intel Corporation Xeon
        E3-1200 v2/3rd Gen Core processor Graphics Controller
        [8086:0152] (rev 09)

        
        Then added to my domain definition:

        
            <hostdev mode='subsystem' type='pci' managed='yes'>

              <source>

                <address domain='0x0000' bus='0x00' slot='0x02'
        function='0x0'/>

              </source>

              <address type='pci' domain='0x0000' bus='0x00'
        slot='0x08' function='0x0'/>

            </hostdev>

        
        With that added code I consistently get "Connection to guest
        failed" messages and the guest fails to start.

        
        /var/log/libvirt/qemu is empty.  No log.

        
        So my 1st question is can I do this given my hardware?  If the
        answer is "yes" then this is where I'm stuck.

        
        Additionally, I tried:

        
        ]$ virsh nodedev-detach pci_0000_00_02_0

        error: Failed to detach device pci_0000_00_02_0

        error: Failed to add PCI device ID '8086 0152' to pci-stub:
        Permission denied

      
    Are you running virsh as root? Is this your only VGA card?

    
        My thinking was simply to verify if I could manually detach the
        device.  I couldn't find a reference searching for this error. 
        Any help would be greatly appreciated!

      
    You haven't indicated what distro/version you're running, but on
    some versions of Fedora at least, you need to configure libvirt to
    run qemu processes as root rather than the qemu user (that wouldn't
    have caused a problem with nodedev-detach though, although a problem
    with selinux could have).

    
    I would suggest trying your experiment after 1) assuring that you're
    running virsh as root, 2) disabling selinux if your system has it,
    3) setting the user/group in /etc/libvirt/qemu.conf to "root" and
    restarting libvirtd. However, since I think it's highly unlikely
    that you'll be successful in any case, I hesitate to use up your
    time doing that.

    
    Good luck.

    
_______________________________________________
libvirt-users mailing list
libvirt-users@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/libvirt-users