Re: [Qemu-devel] storing machine data in qcow images?

[Andrea Bolognani <abologna@redhat.com>]

On Thu, 2018-06-07 at 11:32 +0100, Richard W.M. Jones wrote:
> On Thu, Jun 07, 2018 at 12:02:29PM +0200, Andrea Bolognani wrote:
> > Something that I haven't seen mentioned in the thread - and this
> > looks like as good a point as any to jump in - is that for q35
> > guests using EFI as well as aarch64 guests the "one click import"
> > experience requires not only hints about the machine (and firmware!)
> > type, but also a copy of the EFI variable store:
> > 
> >   $ virt-builder fedora-27 --arch aarch64 --notes
> >   Fedora® 27 Server (aarch64)
> > 
> >   [...]
> > 
> >   You will need to use the associated UEFI NVRAM variables file:
> >     http://libguestfs.org/download/builder/fedora-27-aarch64-nvram.xz
> 
> This is true, although only sometimes.  If the bootloader[*] has a
> working fallback path then usually it is able to boot and reset the
> UEFI varstore back to the correct values.  We have had bugs before
> where the fallback path was not working, eg:
> 
>   https://bugzilla.redhat.com/show_bug.cgi?id=1353689 (yours!)
>   https://bugzilla.redhat.com/show_bug.cgi?id=1558793

[...]
> [*] I'm not sure exactly which bit of the bootloader does this,
> whether it's UEFI itself, or the grub-efi in the guest.

IIUC the UEFI spec itself reserves certain file names in the ESP
for this fallback mechanism; it's then up to the guest operating
system to actually install something appropriate there.

In Fedora and RHEL, shim is what takes care of it (except when it
doesn't ;), but in Debian and Ubuntu AFAIK shim is not included
and the fallback path doesn't work at all, which makes providing
the NVRAM file a hard requirement to boot such guests.

-- 
Andrea Bolognani / Red Hat / Virtualization