Libguestfs - Mar 2018 - Re: Nested KVM on VMware ESXi failure (was: Re: Issue with libguestfs-test-tool on a guest hosted on VMWare ESXi)

Yes it works if I use force_tcg env variable

On Sat, 24 Mar 2018 at 4:37 AM, Richard W.M. Jones <rjones@redhat.com>
wrote:
>
> On Fri, Mar 23, 2018 at 05:35:38PM +0000, Tanmoy Sinha wrote:
> > Thanks. Reading the defect and the associated thread in
> > https://bugs.launchpad.net/qemu/+bug/1661386, I enabled performance
> > counters in VMWare guest settings. Now the kvm assertion `ret =>
> cpu->kvm_msr_buf->nmsrs'  is gone. But the qemu/kvm hangs after
printing
> > "SeaBIOS (version 1.10.2-1)"
> >
> > I presume this too is a qemu/kvm issue for vmware platforms. Is there
any
> > existing issue reported?
>
> Does it work if you set:
>
>   export LIBGUESTFS_BACKEND_SETTINGS=force_tcg
>
> ?
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-builder quickly builds VMs from scratch
> http://libguestfs.org/virt-builder.1.html
>

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.

On Sat, 24 Mar 2018 at 09:46 Tanmoy Sinha <tanmoy.sinha@gmail.com> wrote:
> Yes it works if I use force_tcg env variable
>
> On Sat, 24 Mar 2018 at 4:37 AM, Richard W.M. Jones
<rjones@redhat.com>
> wrote:
>
>>
>> On Fri, Mar 23, 2018 at 05:35:38PM +0000, Tanmoy Sinha wrote:
>> > Thanks. Reading the defect and the associated thread in
>> > https://bugs.launchpad.net/qemu/+bug/1661386, I enabled
performance
>> > counters in VMWare guest settings. Now the kvm assertion `ret
=>> > cpu->kvm_msr_buf->nmsrs'  is gone. But the qemu/kvm
hangs after printing
>> > "SeaBIOS (version 1.10.2-1)"
>> >
>> > I presume this too is a qemu/kvm issue for vmware platforms. Is
there
>> any
>> > existing issue reported?
>>
>> Does it work if you set:
>>
>>   export LIBGUESTFS_BACKEND_SETTINGS=force_tcg
>>
>> ?
>>
>> Rich.
>>
>> --
>> Richard Jones, Virtualization Group, Red Hat
>> http://people.redhat.com/~rjones
>> Read my programming and virtualization blog: http://rwmj.wordpress.com
>> virt-builder quickly builds VMs from scratch
>> http://libguestfs.org/virt-builder.1.html
>>
>

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.

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

[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

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@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
>