Re: freedos under qemu failure with nvmm

[Vitaly Shevtsov <shev.vt1984%gmail.com@localhost>]

Well.. This makes sense actually. At least this sounds true.

On Sat, Nov 15, 2025 at 2:04 PM Ramiro Aceves <ea1abz%gmail.com@localhost> wrote:
>
>
>
> 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.
> >>
> >>
> >>>
> >>>
> >>
>