On Tue, 31 May 2022 at 16:40, Peter Gonda <pgo...@google.com> wrote:
>
> The SEV-ES bit of Fn800-001F[EAX] - Bit 3 is used for a host to
> determine support for running SEV-ES guests. It should not be checked by
> a guest to determine if it is running under SEV-ES. The guest should use
> the SEV_STATUS MSR Bit 1 to determine if SEV-ES is enabled. This check
> was not part of the original SEV-ES support and was added in
> a91b700e38. Removing the check makes this code consistent with the
> Linux kernel
>
> Fixes: a91b700e38 (Ovmf/ResetVector: Simplify and consolidate the SEV
> features checks)
>
> Cc: James Bottomley <j...@linux.ibm.com>
> Cc: Min Xu <min.m...@intel.com>
> Cc: Jiewen Yao <jiewen....@intel.com>
> Cc: Tom Lendacky <thomas.lenda...@amd.com>
> Cc: Jordan Justen <jordan.l.jus...@intel.com>
> Cc: Ard Biesheuvel <ardb+tianoc...@kernel.org>
> Cc: Laszlo Ersek <ler...@redhat.com>
> Cc: Erdem Aktas <erdemak...@google.com>
> Cc: Brijesh Singh <brijesh.si...@amd.com>
> Cc: Erdem Aktas <erdemak...@google.com>
> Cc: Marc Orr <marc...@google.com>
> Signed-off-by: Peter Gonda <pgo...@google.com>
> Acked-by: Tom Lendacky <thomas.lenda...@amd.com>
>
> ---
> OvmfPkg/ResetVector/Ia32/AmdSev.asm | 8 --------
> 1 file changed, 8 deletions(-)
>
> diff --git a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> index 1f827da3b9..77692db27e 100644
> --- a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> +++ b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> @@ -265,14 +265,6 @@ CheckSevFeatures:
> ; Set the work area header to indicate that the SEV is enabled
> mov byte[WORK_AREA_GUEST_TYPE], 1
>
> - ; Check for SEV-ES memory encryption feature:
> - ; CPUID Fn8000_001F[EAX] - Bit 3
> - ; CPUID raises a #VC exception if running as an SEV-ES guest
> - mov eax, 0x8000001f
> - cpuid
> - bt eax, 3
> - jnc GetSevEncBit
> -
> ; Check if SEV-ES is enabled
> ; MSR_0xC0010131 - Bit 1 (SEV-ES enabled)
> mov ecx, SEV_STATUS_MSR
Thanks Peter, I have queued this up.
I did wonder, though: the only remaining reference to GetSevEncBit is
a conditional branch that just precedes the label itself. This appears
to be a leftover from commit 63c50d3ff2854a76 ("OvmfPkg/ResetVector:
cache the SEV status MSR value in workarea") but it looks a bit dodgy.
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