Re: Guest Ubuntu 18.04 fails to boot with -serial mon:stdio, cannot find ttyS0.

[David Fernandez]

Hi Peter,

Answers in line.

On 08/11/2021 19:59, Peter Maydell wrote:
> 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 guest waits at the end forever... probably because it tries to use the
normal console instead and that does not get displayed with my options.

These are all the services that fail:

[ TIME ] Timed out waiting for device dev-ttyS0.device.
[DEPEND] Dependency failed for Serial Getty on ttyS0.
...
[FAILED] Failed to start Dispatcher daemon for systemd-networkd. <== 
network does start fine though.
See 'systemctl status networkd-dispatcher.service' for details.
...
[FAILED] Failed to start Wait until snapd is fully seeded. <== snapd 
runs fine though.
See 'systemctl status snapd.seeded.service' for details.
...
[FAILED] Failed to start Holds Snappy daemon refresh.
See 'systemctl status snapd.hold.service' for details.
[  OK  ] Started Update UTMP about System Runlevel Changes.
... waits forever ...


>> 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 ?

Yes.


> Does the x86-64 host still work OK if you run it with KVM turned off
> (ie matching the aarch64 host setup) ?

Have not tried that... is there an easy way/option to run that test? Or 
do I need
to compile from sources in Fedora?


>
>> 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.
Is there a specific branch I should use? Could not see more than 2.12 in
git.qemu.org regarding stable branches, but happy to compile and try any 
other.

>
> 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).
The machine is a Jetson AGX Xavier, uses a "Volta" CPU with 8 cores.
In theory should be powerful enough, but you tell me, nVidia does not 
offer a
lot of information on their systems anyway.

>>     --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.
Good to learn that... here you are the output of virt-host-validate that I
happened to find about:

$ sudo virt-host-validate
   QEMU: Checking if device /dev/kvm 
exists                                   : FAIL (Check that CPU and 
firmware supports virtualization and kvm module is loaded)
   QEMU: Checking if device /dev/vhost-net 
exists                             : WARN (Load the 'vhost_net' module 
to improve performance of virtio networking)
   QEMU: Checking if device /dev/net/tun 
exists                               : PASS
   QEMU: Checking for cgroup 'memory' controller 
support                      : PASS
   QEMU: Checking for cgroup 'memory' controller 
mount-point                  : PASS
   QEMU: Checking for cgroup 'cpu' controller 
support                         : PASS
   QEMU: Checking for cgroup 'cpu' controller 
mount-point                     : PASS
   QEMU: Checking for cgroup 'cpuacct' controller 
support                     : PASS
   QEMU: Checking for cgroup 'cpuacct' controller 
mount-point                 : PASS
   QEMU: Checking for cgroup 'cpuset' controller 
support                      : PASS
   QEMU: Checking for cgroup 'cpuset' controller 
mount-point                  : PASS
   QEMU: Checking for cgroup 'devices' controller 
support                     : PASS
   QEMU: Checking for cgroup 'devices' controller 
mount-point                 : PASS
   QEMU: Checking for cgroup 'blkio' controller 
support                       : PASS
   QEMU: Checking for cgroup 'blkio' controller 
mount-point                   : PASS
WARN (Unknown if this platform has IOMMU support) <= it does have IOMMU, 
I know for sure from playing with v4l2...
    LXC: Checking for Linux >= 
2.6.26                                         : PASS
    LXC: Checking for namespace 
ipc                                           : PASS
    LXC: Checking for namespace 
mnt                                           : PASS
    LXC: Checking for namespace 
pid                                           : PASS
    LXC: Checking for namespace 
uts                                           : PASS
    LXC: Checking for namespace 
net                                           : PASS
    LXC: Checking for namespace 
user                                          : PASS
    LXC: Checking for cgroup 'memory' controller 
support                      : PASS
    LXC: Checking for cgroup 'memory' controller 
mount-point                  : PASS
    LXC: Checking for cgroup 'cpu' controller 
support                         : PASS
    LXC: Checking for cgroup 'cpu' controller 
mount-point                     : PASS
    LXC: Checking for cgroup 'cpuacct' controller 
support                     : PASS
    LXC: Checking for cgroup 'cpuacct' controller 
mount-point                 : PASS
    LXC: Checking for cgroup 'cpuset' controller 
support                      : PASS
    LXC: Checking for cgroup 'cpuset' controller 
mount-point                  : PASS
    LXC: Checking for cgroup 'devices' controller 
support                     : PASS
    LXC: Checking for cgroup 'devices' controller 
mount-point                 : PASS
    LXC: Checking for cgroup 'blkio' controller 
support                       : PASS
    LXC: Checking for cgroup 'blkio' controller 
mount-point                   : PASS
    LXC: Checking if device /sys/fs/fuse/connections 
exists                   : FAIL (Load the 'fuse' module to enable /proc/ 
overrides)

>
> -- PMM

Thanks for helping.

David