Nested VMX support in qemu and kvm

[Kfir Lavi]

On Tue, Sep 6, 2011 at 3:15 PM, Nadav Har'El <nyh at math.technion.ac.il>wrote:

> On Tue, Sep 06, 2011, Kfir Lavi wrote about "Nested VMX support in qemu and
> kvm":
> > Hi,
>
> Wow, I didn't expect to see a discussion about nested VMX in linux-il?
> Any particular reason why you bring this up here, and not in the KVM
> mailing list?
>
> > I'm trying to use a nested vm, but whatever I do, no vmx flag is in
> > /proc/cpuinfo ?
> > qemu-kvm -cpu host
> > qemu-kvm -cpu host,+vmx
> > qemu-kvm -cpu qemu64,+vmx
>
> As you can see in my original announcement, and also in
> Documentation/virtual/kvm/nested-vmx.txt, nested VMX is still considered
> experimental, and therefore must be enabled explictly not just in qemu
> (which you did correctly) but also in the kernel module: you must load
> the kvm-intel module as:
>
>        insmod kvm-intel.ko nested=1
>
> Since you didn't mention doing this, is it possible you forgot?
>
> If you get an error with the above insmod, it means you are using an old
> version of KVM which didn't yet support nested VMX. Nested VMX was only
> recently integrated with the main tree.
>
> > I'm running Gentoo with kernel 3.0.4 and
>
> I'm not sure what exactly 3.0.4 contains, but it might be too old to
> contain nested VMX. Linux 3.0's cutoff date was already several months
> ago, so I believe nested VMX only made it to Linux 3.1, not 3.0.
>
> Like I said, if insmod with "nested=1" fails, then you have too old
> a module. You can get a newer kernel directly from the KVM repository.
>
> Yes you right, kernel  linux-3.1-rc4 has this patch, and using the nested=1

parameter I'm able to use nested vmx.
It is a really useful feature.
(more info is in Documentation/virtual/kvm/nested-vmx.txt)

Send my regards to the ppl in your team at IBM Hifa,
Kfir

> > I did saw some emails and patches on the net from Orit, Avi and Nadav
> about
> > nested vmx support,
> > but it doesn't seems to work for me.
>
> After 11 (!) rounds of discussions spanning more than a year, Avi accepted
> these patches and nested VMX is now part of the main KVM tree. So please
> use the main KVM tree, not any of the old patches you find on the net, if
> you can.
>
> Good luck,
> Nadav.
>
>
> --
> Nadav Har'El                        |        Tuesday, Sep  6 2011, 7 Elul
> 5771
> nyh at math.technion.ac.il
> |-----------------------------------------
> Phone +972-523-790466, ICQ 13349191 |An egotist is a person of low taste,
> more
> http://nadav.harel.org.il           |interested in himself than in me.
>
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