virtiofs guest connection refused after upgrade qemu-system-x86:amd64 (1:6.2+dfsg-2ubuntu6.12, 1:6.2+dfsg-2ubuntu6.13)

Background Infos:
System: Linux 5.15.0-82-generic #91-Ubuntu SMP Mon Aug 14 14:14:14 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Can you give the exact error please? I'm not seeing the phrase you posted, online

What OS is the host and what OS is the guest too, please?

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

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

if it helps, I can provide the XML-File of the virtual machine as well

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>
...

Are you using ZFS?
https://github.com/openzfs/zfs/issues/14932

No, I am using ext4 and the issue was not there before the upgrades of
qemu-system-x86:amd64
qemu-user-static:amd64
qemu-utils:amd64
qemu-system-common:amd64
qemu-block-extra:amd64
qemu-system-data:amd64
qemu-system-gui:amd64

all from version 1:6.2+dfsg-2ubuntu6.12 to version 1:6.2+dfsg-2ubuntu6.13

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.

I suggest that you create a bug report.

Bug Report created