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

Erdem Aktas
2020-07-21T16:49:08Z

Yes, I am using OVMF with SEV-ES (sev-es-v12 patches applied). I am
running Ubuntu 18.04 distro. My grub target is x86_64-efi. I also
tried installing the grub-efi-amd64 package. In all cases, the grub is
running in 64bit but enters the startup_32 in 32 bit mode. I think
there should be a 32bit #VC handler just something very similar in the
OVMF patches to handle the cpuid when the CPU is still in 32bit mode.
As it is now, it will be a huge problem to support different distro images.
I wonder if I am the only one having this problem.

-Erdem

On Tue, Jul 21, 2020 at 5:50 AM Joerg Roedel <jroedel@suse.de> wrote:
>
> 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
>