Initialization of device cfi.pflash01 failed: Block node is read-only

Hi,

I have several vms defined in libvirt using ovmf for uefi, since a later
update of my server I'm unable to start any of the domains defined. This is
an example of the output given:

# virsh start os-1
error: Failed to start domain os-1
error: internal error: qemu unexpectedly closed the monitor: 2019-03-02T21:23:51.726446Z qemu-system-x86_64: Initialization of device cfi.pflash01 failed: Block node is read-only

an example of domain is like this:

<domain type='kvm'>                                                                                                                                                                                                                                                            
  <name>os-1</name>                                                                                                                                                                                                                                                            
  <uuid>34c41008-ab91-483b-959c-81a7a12ae9be</uuid>                                                                                                                                                                                                                            
  <memory unit='KiB'>8388608</memory>                                                                                                                                                                                                                                          
  <currentMemory unit='KiB'>8388608</currentMemory>                                                                                                                                                                                                                            
  <memoryBacking>                                                                                                                                                                                                                                                              
    <hugepages/>                                                                                                                                                                                                                                                               
  </memoryBacking>                                                                                                                                                                                                                                                             
  <vcpu placement='static' cpuset='10-11,34-35'>4</vcpu>                                                                                                                                                                                                                       
  <os>                                                                                                                                                                                                                                                                         
    <type arch='x86_64' machine='pc-i440fx-2.12'>hvm</type>                                                                                                                                                                                                                    
    <loader type='pflash'>/var/lib/libvirt/qemu/nvram/os-1-ovmf.fd</loader>                                                                                                                                                                                                    
    <boot dev='network'/>                                                                                                                                                                                                                                                      
    <boot dev='hd'/>                                                                                                                                                                                                                                                           
  </os>                                                                                                                                                                                                                                                                        
  <features>                                                                                                                                                                                                                                                                   
    <acpi/>                                                                                                                                                                                                                                                                    
    <apic/>                                                                                                                                                                                                                                                                    
  </features>                                                                                                                                                                                                                                                                  
  <cpu mode='host-passthrough' check='partial'/>                                                                                                                                                                                                                               
  <clock offset='utc'>                                                                                                                                                                                                                                                         
    <timer name='rtc' tickpolicy='catchup'/>                                                                                                                                                                                                                                   
    <timer name='pit' tickpolicy='delay'/>                                                                                                                                                                                                                                     
    <timer name='hpet' present='no'/>                                                                                                                                                                                                                                          
  </clock>                                                                                                                                                                                                                                                                     
  <on_poweroff>destroy</on_poweroff>                                                                                                                                                                                                                                           
  <on_reboot>restart</on_reboot>                                                                                                                                                                                                                                               
  <on_crash>destroy</on_crash>                                                                                                                                                                                                                                                 
  <pm>                                                                                                                                                                                                                                                                         
    <suspend-to-mem enabled='no'/>                                                                                                                                                                                                                                             
    <suspend-to-disk enabled='no'/>                                                                                                                                                                                                                                            
  </pm>                                                                                                                                                                                                                                                                        
  <devices>                                                                                                                                                                                                                                                                    
    <emulator>/usr/bin/qemu-system-x86_64</emulator>                                                                                                                                                                                                                           
    <disk type='block' device='disk'>                                                                                                                                                                                                                                          
      <driver name='qemu' type='raw' cache='none' io='native'/>                                                                                                                                                                                                                
      <source dev='/dev/vg0/os-1-vda'/>                                                                                                                                                                                                                                   
      <target dev='vda' bus='virtio'/>                                                                                                                                                                                                                                         
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>                                                                                                                                                                                              
    </disk>                                                                                                                                                                                                                                                                    
    <disk type='block' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='native'/>
      <source dev='/dev/vg0/os-1-vdb'/>
      <target dev='vdb' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:78:cb:97'/>
      <source bridge='virbr0'/>
      <model type='rtl8139'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </interface>
    <interface type='bridge'>
      <mac address='52:54:00:1c:4f:22'/>
      <source bridge='virbr1'/>
      <model type='rtl8139'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target type='isa-serial' port='0'>
        <model name='isa-serial'/>
      </target>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'>
      <listen type='address'/>
    </graphics>
    <video>
      <model type='cirrus' vram='16384' heads='1' primary='yes'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
    </memballoon>
  </devices>
</domain>

where /var/lib/libvirt/qemu/nvram/os-1-ovmf.fd is a copy of
/usr/share/edk2-ovmf/OVMF_VARS.fd. An the extract from my
/etc/libvirt/qemu.conf to define ovmf:

...
# Location of master nvram file                                                                                                                                                                                                                                                
#                                                                                                                                                                                                                                                                              
# When a domain is configured to use UEFI instead of standard                                                                                                                                                                                                                  
# BIOS it may use a separate storage for UEFI variables. If                                                                                                                                                                                                                    
# that's the case libvirt creates the variable store per domain                                                                                                                                                                                                                
# using this master file as image. Each UEFI firmware can,                                                                                                                                                                                                                     
# however, have different variables store. Therefore the nvram is                                                                                                                                                                                                              
# a list of strings when a single item is in form of:                                                                                                                                                                                                                          
#   ${PATH_TO_UEFI_FW}:${PATH_TO_UEFI_VARS}.                                                                                                                                                                                                                                   
# Later, when libvirt creates per domain variable store, this list is                                                                                                                                                                                                          
# searched for the master image. The UEFI firmware can be called                                                                                                                                                                                                               
# differently for different guest architectures. For instance, it's OVMF                                                                                                                                                                                                       
# for x86_64 and i686, but it's AAVMF for aarch64. The libvirt default                                                                                                                                                                                                         
# follows this scheme.                                                                                                                                                                                                                                                         
nvram = [                                                                                                                                                                                                                                                                      
   "/usr/share/edk2-ovmf/OVMF_CODE.fd:/usr/share/edk2-ovmf/OVMF_VARS.fd",                                                                                                                                                                                                      
]
...

This setup used to work one month ago, now it's setup with:

QEMU emulator version 3.1.0
libvirt-5.0.0
linux-4.19.20

Any help appreciated.

Best regards.

José