Comment 0 for bug 2033957

After installing the upgrades
qemu-system-x86:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-user-static:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-utils:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-system-common:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-block-extra:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-system-data:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13),
qemu-system-gui:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13)

and a reboot of the server, all virtual machines are getting an "connection refused" error and cannot access the host folders via virtiofs anymore.

Exact Error message on the client:
cannot access '/var/www-lib': Connection refused

Nothing else in the Logs.
Client OS:
Distributor ID: Ubuntu
Description: Ubuntu 22.04.3 LTS
Release: 22.04
Codename: jammy
Linux 5.15.0-82-generic #91-Ubuntu SMP
FileSystem: EXT4

Server OS:
Distributor ID: Ubuntu
Description: Ubuntu 22.04.3 LTS
Release: 22.04
Codename: jammy
Ubuntu 22.04, 5.15.0-82-generic #91-Ubuntu SMP Mon Aug 14 14:14:14 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
FileSystem: EXT4

I scanned all logs, in the kern.log, I found the following message:

virtiofs virtio0: virtio_fs_setup_dax: No cache capability

the XML-Code from the guest machine looks like this:

...
  <memoryBacking>
    <hugepages>
      <page size='2' unit='M'/>
    </hugepages>
    <access mode='shared'/>
  </memoryBacking>
....
    <filesystem type='mount' accessmode='passthrough'>
      <driver type='virtiofs' queue='1024'/>
      <binary path='/usr/lib/qemu/virtiofsd' xattr='on'>
        <cache mode='always'/>
        <lock posix='on' flock='on'/>
      </binary>
      <source dir='/Da/n/W/w'/>
      <target dir='W'/>1
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
    </filesystem>
...

I did a little more trying to find the issue. The change in the file /usr/lib/qemu/virtiofsd with the update 1:6.2+dfsg-2ubuntu6.13 is causing the problem.
I did an upgrade to the new rust based virtiofsd and modified my virtual machine to be loaded without flock and posix on.
Voila, mapping is working.
Now I changed it back to the original version - access denied
flock and posix still not configured, changing back to version 1:6.2+dfsg-2ubuntu6.12 is also working.

Therefore I assume we have an bug in the new virtiofsd version.