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From:   Erdem Aktas <erdemaktas@google.com>
Date:   Tue, 21 Jul 2020 09:48:51 -0700
Message-ID: <CAAYXXYwVV_g8pGL52W9vxkgdNxg1dNKq_OBsXKZ_QizdXiTx2g@mail.gmail.com>
Subject: Re: [PATCH v4 00/75] x86: SEV-ES Guest Support
To:     Joerg Roedel <jroedel@suse.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Joerg Roedel <joro@8bytes.org>, x86@kernel.org, hpa@zytor.com,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jiri Slaby <jslaby@suse.cz>,
        Dan Williams <dan.j.williams@intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Juergen Gross <jgross@suse.com>,
        Kees Cook <keescook@chromium.org>,
        David Rientjes <rientjes@google.com>,
        Cfir Cohen <cfir@google.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mike Stunes <mstunes@vmware.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Martin Radev <martin.b.radev@gmail.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org
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Sender: linux-kernel-owner@vger.kernel.org
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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
>