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kbase: More info on firmware change for existing VMs

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The need to remove the <loader> and <nvram> elements in order
to make the firmware autoselection process kick in again is
not exactly intuitive, so document it explicitly.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
This commit is contained in:
Andrea Bolognani 2023-11-16 17:01:44 +01:00
parent 65bf8fc9cf
commit b31380c758
1 changed files with 25 additions and 5 deletions
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30
docs/kbase/secureboot.rst
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@ -72,16 +72,36 @@ relevant documentation
Changing an existing VM
=======================
Once the VM has been created, updating the XML configuration as
described above is **not** enough to change the Secure Boot status:
the NVRAM file associated with the VM has to be regenerated from its
template as well.
When a VM is defined, libvirt will pick the firmware that best
satisfies the provided criteria and record this information for use
on subsequent boots. The resulting XML configuration will look like
this:
::
<os firmware='efi'>
<firmware>
<feature enabled='yes' name='enrolled-keys'/>
<feature enabled='yes' name='secure-boot'/>
</firmware>
<loader readonly='yes' secure='yes' type='pflash'>/usr/share/edk2/ovmf/OVMF_CODE.secboot.fd</loader>
<nvram template='/usr/share/edk2/ovmf/OVMF_VARS.secboot.fd'>/var/lib/libvirt/qemu/nvram/vm_VARS.fd</nvram>
</os>
In order to force libvirt to repeat the firmware autoselection
process, it's necessary to remove the ``<loader>`` and ``<nvram>``
elements. Failure to do so will likely result in an error.
Note that updating the XML configuration as described above is
**not** enough to change the Secure Boot status: the NVRAM file
associated with the VM has to be regenerated from its template as
well.
In order to do that, update the XML and then start the VM with
::
$ virsh start $vm --reset-nvram
$ virsh start vm --reset-nvram
This option is only available starting with libvirt 8.1.0, so if your
version of libvirt is older than that you will have to delete the