[Libguestfs] Nested KVM on VMware ESXi failure (was: Re: Issue with libguestfs-test-tool on a guest hosted on VMWare ESXi)

[Tanmoy Sinha]

I am trying that out. Debian 9 (stretch) backports still doesn't have 4.16
kernel.

So I building the kernel from the source. Will keep you posted.

On Mon, 26 Mar 2018 at 13:00 Richard W.M. Jones <rjones at redhat.com> wrote:

> [Adding Paolo and Vitaly, but FYI only as the bug seems to have an
> upstream fix already.]
>
> On Mon, Mar 26, 2018 at 09:13:45AM +0300, Roman Kagan wrote:
> > On Sat, Mar 24, 2018 at 03:11:12PM +0000, Richard W.M. Jones wrote:
> > > On Sat, Mar 24, 2018 at 03:08:16PM +0000, Tanmoy Sinha wrote:
> > > > Even though force_tcg works, I intend not to run it on emulation. Is
> there
> > > > way I can run it over kvm? The other observation is, without
> force_tcg if I
> > > > use the machine type as  *pc-i440fx-2.**1*,accel=kvm it works fine.
> The
> > > > default machine type for my host *pc-i440fx-2.8, *which seems to
> crib.
> > >
> > > I don't know, but this is basically a bug in VMware, so you need
> > > to ask them to fix their nested KVM-on-ESXi use case.
> >
> > We've encountered this problem, too.
> >
> > Strictly speaking, the bug is not in VMWare, but rather in KVM: on
> > EPT_MISCONFIG vmexits it assumed the processor to set the instuction
> > length field.  This wasn't mandated by the spec but the real processors
> > did that.  OTOH some hypervisors (VMWare, Hyper-V) didn't do that for
> > the nested hypervisor.  As a result, when handling MMIO the guest
> > instruction pointer didn't get advanced, i.e. the guest got stuck in an
> > infinite loop.
> >
> > The difference between the old and the new machine type is that the
> > latter turns on newer virtio protocol version employing MMIO, exposing
> > this bug.
> >
> > The fix is commit d391f1207067268261add0485f0f34503539c5b0 which went
> > into 4.16-rc1.
>
> Can you (Tanmoy) please try a newer kernel inside the VMware guest?
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>
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