Itamar, can you provide additional detail as to what is required from libvirt?

(In reply to comment #3)
> Itamar, can you provide additional detail as to what is required from libvirt?

to allow setting the enable (or disable) ksm per VM per the blocking BZ on KVM
(same for THP in another BZ)

I will write poposal to upstream libvir-list first, then patches.

- Osier

with detection, and confirmed with Dor and danpb, it should be "command line argument" instead of "qemu monitor command", and it's still not implemented in qemu-kvm yet.

- Osier

http://post-office.corp.redhat.com/archives/rhvirt-patches/2011-January/msg00322.html

patch posted to rhvirt-patches

the final patch sent internally:

http://post-office.corp.redhat.com/archives/rhvirt-patches/2011-February/msg00660.html

Verified pass on libvirt-0.8.7-6.el6.x86_64
- kernel-2.6.32-113.el6.x86_64

------ Positive testing ------
- qemu-kvm-0.12.1.2-2.144.el6.x86_64

1. Add the following xml info into guest 
  <memoryBacking>
    <nosharepages/>
  </memoryBacking>
2. Start the guest
# virsh start rhel6
3. # ps aux|grep kvm | grep ksm -i
qemu      8063  9.0  4.7 1330152 376908 ?      Sl   21:11   0:38 /usr/libexec/qemu-kvm -S -M rhel6.1.0 -enable-kvm -m 1024 
-redhat-disable-KSM 
-smp 1,sockets=1,cores=1,threads=1 -name rhel6 -uuid 092dcbfe-ec20-9ff6-9a34-4c516c233e33 -nodefconfig -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/rhel6.monitor,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -boot c -drive file=/var/lib/libvirt/images/rhel6.img,if=none,id=drive-virtio-disk0,format=raw,cache=none -device virtio-blk-pci,bus=pci.0,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0 -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=26 -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:3f:c4:20,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -usb -device usb-tablet,id=input0 -vnc 127.0.0.1:0 -vga cirrus -device AC97,id=sound0,bus=pci.0,addr=0x4 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6

Verified pass on libvirt-0.8.7-6.el6.x86_64
- kernel-2.6.32-71.el6.x86_64

------ Negative testing ------
- qemu-kvm-0.12.1.2-2.113.el6.x86_64

1. Add the following xml info into guest 
  <memoryBacking>
    <nosharepages/>
  </memoryBacking>
2. Start the guest
# virsh start rhel6
error: Failed to start domain rhel6
error: internal error '-redhat-disable-KSM' is not supported by '/usr/libexec/qemu-kvm'

    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
This update allows user disable memory merging (KSM) of guest, (by default, qemu-kvm enables KSM for guest), NB, it needs underly qemu-kvm supports "-redhat-disable-KSM" flag.

    Technical note updated. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    Diffed Contents:
@@ -1 +1 @@
-This update allows user disable memory merging (KSM) of guest, (by default, qemu-kvm enables KSM for guest), NB, it needs underly qemu-kvm supports "-redhat-disable-KSM" flag.+Users can now disable memory merging (KSM) on guest machines. Note however that this requires support for the underlying qemu-kvm "-redhat-disable-KSM" flag.

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2011-0596.html