[kata-dev] Booting OVMF with -bios?

Laszlo Ersek lersek at redhat.com
Wed Jan 6 17:07:34 UTC 2021

Hi Christophe!

On 01/06/21 16:11, Christophe de Dinechin wrote:
> Hello Laszlo,
> Happy New Year!

Same to you :)

> I may need to pick your brain a little regarding an issue someone testing
> AMD SEV ran into with Kata.
> Basically, here are the questions I have:
> 1) Is it OK to pass an OVMF firmware to the -boot option of qemu?
>    What about SecureBoot in that case?
> 2) Are there any expected behavioral differences between booting with the
>    -bios option and using a -drive if=pflash option? In particular, anything
>    that could prevent SEV from activating in the guest kernel?
> 3) Knowing that in the Kata case, we don't care about anything persisting
>    across reboots, is there any problem passing only the OVMF_CODE.fd image
>    readonly using the -drive option, without having an OVMF_VARS.fd? Asking
>    to see if we need to create an OVMF_VARS.fd for each container.
> If you need a bit of context:
> https://github.com/kata-containers/kata-containers/issues/1231 and
> http://lists.katacontainers.io/pipermail/kata-dev/2021-January/001638.html

"-bios" should never be used with OVMF. If you don't need non-volatile
UEFI variables to persist from one boot of the domain to the next,
that's fine; in that case, please use a throw-away regular file for the
variable store pflash chip. this file should be instantiated from
"OVMF_VARS.fd", if you don't want the Secure Boot operational mode
enabled right off the bat; otherwise, please copy (create) the domain's
varstore from "OVMF_VARS.secboot.fd", before launching QEMU.

We have never tested SEV with "-bios" (well, because "-bios" is wrong to
use with OVMF in the first place, regardless of SEV); and yes there have
been SEV-related changes, specific to the flash driver in OVMF. (QEMU
too received SEV-related changes around the parts responsible for
loading OVMF, in "hw/i386/pc_sysfw.c".)

The particulars of a SEV failure, when using "-bios", aren't even worth
investigating -- please try to reproduce the issue first with two pflash


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