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

[Tanmoy Sinha]

*It works*.

I built and deployed the linux 4.16.0-rc7 kernel on my debian 9 guest
running over VMWare. Now libguestfs-test-tool just works fine when qemu
picks the default machine type pc-i440fx-2.8

$> uname -a

Linux tanmoy-deb-host 4.16.0-rc7 #1 SMP Mon Mar 26 09:52:54 UTC 2018 x86_64
GNU/Linux

On Mon, 26 Mar 2018 at 16:52 Tanmoy Sinha <tanmoy.sinha at gmail.com> wrote:

> 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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