Re: [PATCH v4 00/75] x86: SEV-ES Guest Support

Joerg Roedel
2020-07-21T12:50:03Z

Hi,

On Mon, Jul 20, 2020 at 06:09:19PM -0700, Erdem Aktas wrote:
> It looks like there is an expectation that the bootloader will start
> from the 64bit entry point in header_64.S. With the current patch
> series, it will not boot up if the bootloader jumps to the startup_32
> entry, which might break some default distro images.
> What are supported bootloaders and configurations?
> I am using grub ( 2.02-2ubuntu8.15) and it fails to boot because of
> this reason. I am not a grub expert, so I would appreciate any
> pointers on this.

This is right, the only supported boot path is via the 64bit EFI entry
point. The reason is that SEV-ES requires support in the firmware too,
and currently only OVMF is supported in that regard. The firmware needs
to setup the AP jump-table, for example.

Other boot-paths have not been implemented. Booting via startup_32 would
require exception handling in the 32bit-part of the boot-strap code,
because verify_cpu is called there. Also an AMD specific MSR can't be
accessed there because this would #GP on non-AMD/SEV-ES machines and,
as I said, there is no way yet to handle them.

How did you get into the startup_32 entry-point, do you have an SEV-ES
BIOS supporting this? If it is really needed it could be implemented at
a later point.

Regards,

Joerg