Re: freedos under qemu failure with nvmm

[Ramiro Aceves <ea1abz%gmail.com@localhost>]

El 15/11/25 a las 9:52, Vitaly Shevtsov escribió:
> Hello, Ramiro.
>
> I don't know the reason. It looks like FreeDOS uses something that
> other OSes don't use causing QEMU to crash.
> But for me it happens only when FreeDOS is being installed. Once it's
> installed I never face this issue. I'm pretty sure it's a bug in NVMM.
> Maybe it's worth trying dosbox instead?

Hi Vitaly!

dosbox works fine but it is a different thing, you know...
I have been several hour fighting with this, Chatgpt says the following 
but I cannot trust him  ;-)

"NVMM’s early implementations had — and still have — some rough edges in 
handling certain 16-bit BIOS calls or transitions between real mode and 
protected mode."

FreeDOS wants to boot in 16-bit real mode and use old hardware 
peripherals (keyboard controller, PIT timer, SB16 sound card).

QEMU normally emulates all of that correctly.

NVMM, however, is designed for modern x86-64 virtualization, and it 
cannot execute a VCPU correctly while it is in 16-bit real mode.

Result:
QEMU aborts with “Failed to execute a VCPU.”

I do not know if it is true or not, many times Chatgpt say silly things  ;-)


Regards.
Ramiro.


> On Thu, Nov 13, 2025 at 11:29 PM Ramiro Aceves <ea1abz%gmail.com@localhost> wrote:
> > El 13/11/25 a las 19:19, Vitaly Shevtsov escribió:
> > > Hello. I faced the same issue with qemu, nvmm and freedos. Tried to
> > > debug with no luck. I found a workaround - run qemu with no
> > > acceleration, install freedos, then run it with acceleration turned on.
> > > This issue only happens when is it is being installed.
> > >
> > > чт, 13 нояб. 2025 г., 23:15 Ramiro Aceves <ea1abz%gmail.com@localhost
> > > <mailto:ea1abz%gmail.com@localhost>>:
> > >
> > >
> > >      Hello,
> > >
> > >      I tried to install FreeDOS under Qemu in NetBSD 10.1 using nvmm
> > >      acceleration driver.
> > >
> > >
> > >      I get an error like this when almost installed on the virtual disk:
> > >
> > >      qemu-system-i386: NVMM: Unexpected VM exit code 0xffffffffffffffff
> > >      [hw=0x9]
> > >      qemu-system-i386: NVMM: Failed to execute a VCPU.
> > >      [1]   Abort trap (core dumped) qemu-system-i386 -m 64 -accel nvmm -
> > >      smp 1
> > >      -dri...
> > >
> > >
> > >      I removed nvmm acceleration and I was able to end the installation
> > >      without acceleration but it was painly slow.
> > >
> > >      I have been able to virtualize a full Debian GNU/Linux system using
> > >      nvmm, no problems at all. Why nvmm fails with FreeDOS?
> > >
> > >      Thanks so much.
> > >      Ramiro.
> >
> > Hello Vitaly,
> >
> > I have started the virtual FreeDOS with nvmm, it starts fast and well.
> >
> >
> > c:\dir (file listing works fine)
> >
> > But when I start an editor:
> >
> >
> > c:\EDIT
> >
> > qemu-system-i386: NVMM: Failed to execute a VCPU.
> > [1]   Abort trap (core dumped) qemu-system-i386 -m 64 -accel nvmm -smp 1
> > -dri...
> > netbsd-nuc$
> >
> >
> > Regards.
> > Ramiro.
> >
> >
> > >