While looking carefully, I found an error in this and next patch, I will send
a follow up patch to address it. SEV status and GHCB MSR value are very close
and I missed it and used SEV_STATUS_MSR for both case. It should look like this
and used accordingly.
%define SEV_STATUS_MSR 0xc0010130
%define SEV_GHCB_MSR 0xc0010131
On 6/28/2021 12:41 PM, Brijesh Singh wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275
>
> The upcoming SEV-SNP support will need to make a few additional MSR
> protocol based VMGEXIT's. Add a macro that wraps the common setup and
> response validation logic in one place to keep the code readable.
>
> While at it, define SEV_STATUS_MSR that will be used to get the SEV STATUS
> MSR instead of open coding it.
>
> 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>
> Suggested-by: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> OvmfPkg/ResetVector/Ia32/AmdSev.asm | 69 +++++++++++++++++++----------
> 1 file changed, 45 insertions(+), 24 deletions(-)
>
> diff --git a/OvmfPkg/ResetVector/Ia32/AmdSev.asm b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> index b32dd3b5d656..c3b4e16bf681 100644
> --- a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> +++ b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
> @@ -35,6 +35,42 @@ BITS 32
> %define GHCB_CPUID_REGISTER_SHIFT 30
> %define CPUID_INSN_LEN 2
>
> +%define SEV_STATUS_MSR 0xc0010130
> +
> +; Macro is used to issue the MSR protocol based VMGEXIT. The caller is
> +; responsible to populate values in the EDX:EAX registers. After the vmmcall
> +; returns, it verifies that the response code matches with the expected
> +; code. If it does not match then terminate the guest. The result of request
> +; is returned in the EDX:EAX.
> +;
> +; args 1:Request code, 2: Response code
> +%macro VmgExit 2
> + ;
> + ; Add request code:
> + ; GHCB_MSR[11:0] = Request code
> + or eax, %1
> +
> + mov ecx, SEV_STATUS_MSR
> + wrmsr
> +
> + ; Issue VMGEXIT - NASM doesn't support the vmmcall instruction in 32-bit
> + ; mode, so work around this by temporarily switching to 64-bit mode.
> + ;
> +BITS 64
> + rep vmmcall
> +BITS 32
> +
> + mov ecx, SEV_STATUS_MSR
> + rdmsr
> +
> + ;
> + ; Verify the reponse code, if it does not match then request to terminate
> + ; GHCB_MSR[11:0] = Response code
> + mov ecx, eax
> + and ecx, 0xfff
> + cmp ecx, %2
> + jne SevEsUnexpectedRespTerminate
> +%endmacro
>
> ; Check if Secure Encrypted Virtualization (SEV) features are enabled.
> ;
> @@ -85,7 +121,7 @@ CheckSevFeatures:
>
> ; Check if SEV memory encryption is enabled
> ; MSR_0xC0010131 - Bit 0 (SEV enabled)
> - mov ecx, 0xc0010131
> + mov ecx, SEV_STATUS_MSR
> rdmsr
> bt eax, 0
> jnc NoSev
> @@ -100,7 +136,7 @@ CheckSevFeatures:
>
> ; Check if SEV-ES is enabled
> ; MSR_0xC0010131 - Bit 1 (SEV-ES enabled)
> - mov ecx, 0xc0010131
> + mov ecx, SEV_STATUS_MSR
> rdmsr
> bt eax, 1
> jnc GetSevEncBit
> @@ -197,10 +233,10 @@ SevEsIdtNotCpuid:
> mov eax, 1
> jmp SevEsIdtTerminate
>
> -SevEsIdtNoCpuidResponse:
> +SevEsUnexpectedRespTerminate:
> ;
> ; Use VMGEXIT to request termination.
> - ; 2 - GHCB_CPUID_RESPONSE not received
> + ; 2 - Unexpected Response is received
> ;
> mov eax, 2
>
> @@ -216,7 +252,7 @@ SevEsIdtTerminate:
> shl eax, 16
> or eax, 0x1100
> xor edx, edx
> - mov ecx, 0xc0010130
> + mov ecx, SEV_STATUS_MSR
> wrmsr
> ;
> ; Issue VMGEXIT - NASM doesn't support the vmmcall instruction in 32-bit
> @@ -276,7 +312,7 @@ SevEsIdtVmmComm:
> mov [esp + VC_CPUID_REQUEST_REGISTER], eax
>
> ; Save current GHCB MSR value
> - mov ecx, 0xc0010130
> + mov ecx, SEV_STATUS_MSR
> rdmsr
> mov [esp + VC_GHCB_MSR_EAX], eax
> mov [esp + VC_GHCB_MSR_EDX], edx
> @@ -293,31 +329,16 @@ NextReg:
> jge VmmDone
>
> shl eax, GHCB_CPUID_REGISTER_SHIFT
> - or eax, GHCB_CPUID_REQUEST
> mov edx, [esp + VC_CPUID_FUNCTION]
> - mov ecx, 0xc0010130
> - wrmsr
>
> - ;
> - ; Issue VMGEXIT - NASM doesn't support the vmmcall instruction in 32-bit
> - ; mode, so work around this by temporarily switching to 64-bit mode.
> - ;
> -BITS 64
> - rep vmmcall
> -BITS 32
> + VmgExit GHCB_CPUID_REQUEST, GHCB_CPUID_RESPONSE
>
> ;
> - ; Read GHCB MSR
> + ; Response GHCB MSR
> ; GHCB_MSR[63:32] = CPUID register value
> ; GHCB_MSR[31:30] = CPUID register
> ; GHCB_MSR[11:0] = CPUID response protocol
> ;
> - mov ecx, 0xc0010130
> - rdmsr
> - mov ecx, eax
> - and ecx, 0xfff
> - cmp ecx, GHCB_CPUID_RESPONSE
> - jne SevEsIdtNoCpuidResponse
>
> ; Save returned value
> shr eax, GHCB_CPUID_REGISTER_SHIFT
> @@ -335,7 +356,7 @@ VmmDone:
> ;
> mov eax, [esp + VC_GHCB_MSR_EAX]
> mov edx, [esp + VC_GHCB_MSR_EDX]
> - mov ecx, 0xc0010130
> + mov ecx, SEV_STATUS_MSR
> wrmsr
>
> mov eax, [esp + VC_CPUID_RESULT_EAX]
>
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