[edk2-devel] [PATCH v2] OvmfPkg/ResetVector: Removing SEV-ES CPUID bit check

Peter Gonda via groups.io posted 1 patch 1 week, 4 days ago
Failed in applying to current master (apply log)
OvmfPkg/ResetVector/Ia32/AmdSev.asm | 8 --------
1 file changed, 8 deletions(-)

[edk2-devel] [PATCH v2] OvmfPkg/ResetVector: Removing SEV-ES CPUID bit check

Posted by Peter Gonda via groups.io 1 week, 4 days ago
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 <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Marc Orr <marcorr@google.com>
Signed-off-by: Peter Gonda <pgonda@google.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
-- 
2.34.1.575.g55b058a8bb-goog



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Re: [edk2-devel] [PATCH v2] OvmfPkg/ResetVector: Removing SEV-ES CPUID bit check

Posted by Lendacky, Thomas via groups.io 5 days, 12 hours ago
On 1/13/22 10:30 AM, Peter Gonda 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 <jejb@linux.ibm.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Erdem Aktas <erdemaktas@google.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Erdem Aktas <erdemaktas@google.com>
> Cc: Marc Orr <marcorr@google.com>
> Signed-off-by: Peter Gonda <pgonda@google.com>

Acked-by: Tom Lendacky <thomas.lendacky@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
> 


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