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Re: Guest Ubuntu 18.04 fails to boot with -serial mon:stdio, cannot find

From: Peter Maydell
Subject: Re: Guest Ubuntu 18.04 fails to boot with -serial mon:stdio, cannot find ttyS0.
Date: Mon, 8 Nov 2021 19:59:06 +0000

On Mon, 8 Nov 2021 at 18:05, David Fernandez <david.fernandez@sen.com> wrote:
> I am running qemu-system-x86_64 on aarch64 running Ubuntu 18.04 as both
> guest and host.
> I couldn't get the stock qemu-system-x86_04 to boot correctly, as it was
> an old version 2.11.1, I decided to recompile from sources to see if
> that would fix the problem, but the problem still persists, using both
> top of master and stable-2.12 (currently on that).[ TIME ] Timed out
> waiting for device dev-ttyS0.device.

Is there any more error message ? How long does the guest wait on
this step before it times out ?

> The problem does not happen when using qemu-system-x86_64 on my Fedora
> desktop as host, so I wonder if I need something in my build options or
> if I need to rebuild my kernel with some added kernel configuration
> options...

Are you testing with the exact same:
 * command line
 * files (guest kernel, initrd, iso, etc)
 * QEMU version
on both the aarch64 and x86-64 host ?
Does the x86-64 host still work OK if you run it with KVM turned off
(ie matching the aarch64 host setup) ?

> Hopefully, some experts around here can help me with that if it is a
> known thing (I google around but other than mentioning that 2.11 is too
> old, could not find any clear reason about this problem).

For aarch64 host, I would be a bit dubious about running 2.11 or 2.12 --
they are both absolutely ancient in QEMU terms.

What are the specs of the host CPU (in particular, how fast is it)?
If it's too underpowered it's possible it just can't run the guest
fast enough for it to boot up before the guest's systemd tasks
time out (though it would have to be pretty bad for this to be
the problem).

>    --enable-kvm \ <== does not seem to ba available as an accelerator

That is expected -- KVM can only accelerate guests where the
host and guest are the same CPU architecture, so it can do
aarch64-on-aarch64 and x86-on-x86, but not x86-on-aarch64.

-- PMM

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