Re: [edk2-devel] [PATCH v13 07/46] MdePkg/BaseLib: Add support for the VMGEXIT instruction

["Laszlo Ersek" <lersek@redhat.com>]

On 07/30/20 20:43, Lendacky, Thomas wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
> 
> VMGEXIT is a new instruction used for Hypervisor/Guest communication when
> running as an SEV-ES guest. A VMGEXIT will cause an automatic exit (AE)
> to occur, resulting in a #VMEXIT with an exit code value of 0x403.
> 
> Since SEV-ES is only supported in X64, provide the necessary X64 support
> to execute the VMGEXIT instruction, which is coded as "rep vmmcall". For
> IA32, since "vmmcall" is not supported in NASM 32-bit mode and VMGEXIT
> should never be called, provide a stub implementation that is identical
> to CpuBreakpoint().
> 
> Cc: Michael D Kinney <michael.d.kinney@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  MdePkg/Library/BaseLib/BaseLib.inf       |  2 ++
>  MdePkg/Include/Library/BaseLib.h         | 14 +++++++++
>  MdePkg/Library/BaseLib/Ia32/VmgExit.nasm | 38 ++++++++++++++++++++++++
>  MdePkg/Library/BaseLib/X64/VmgExit.nasm  | 32 ++++++++++++++++++++
>  4 files changed, 86 insertions(+)
>  create mode 100644 MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
>  create mode 100644 MdePkg/Library/BaseLib/X64/VmgExit.nasm
> 
> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
> index 3b93b5db8d24..3b85c56c3c03 100644
> --- a/MdePkg/Library/BaseLib/BaseLib.inf
> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> @@ -184,6 +184,7 @@ [Sources.Ia32]
>    Ia32/DisableCache.nasm| GCC
>    Ia32/RdRand.nasm
>    Ia32/XGetBv.nasm
> +  Ia32/VmgExit.nasm
>  
>    Ia32/DivS64x64Remainder.c
>    Ia32/InternalSwitchStack.c | MSFT
> @@ -317,6 +318,7 @@ [Sources.X64]
>    X64/DisablePaging64.nasm
>    X64/RdRand.nasm
>    X64/XGetBv.nasm
> +  X64/VmgExit.nasm
>    ChkStkGcc.c  | GCC
>  
>  [Sources.EBC]
> diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
> index 7edf0051a0a0..04fb329eaabb 100644
> --- a/MdePkg/Include/Library/BaseLib.h
> +++ b/MdePkg/Include/Library/BaseLib.h
> @@ -7848,6 +7848,20 @@ AsmXGetBv (
>    );
>  
>  
> +/**
> +  Executes a VMGEXIT instruction (VMMCALL with a REP prefix)
> +
> +  Executes a VMGEXIT instruction. This function is only available on IA-32 and
> +  x64.
> +
> +**/
> +VOID
> +EFIAPI
> +AsmVmgExit (
> +  VOID
> +  );
> +
> +
>  /**
>    Patch the immediate operand of an IA32 or X64 instruction such that the byte,
>    word, dword or qword operand is encoded at the end of the instruction's
> diff --git a/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm b/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
> new file mode 100644
> index 000000000000..69f7fbf3506a
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/Ia32/VmgExit.nasm
> @@ -0,0 +1,38 @@
> +;------------------------------------------------------------------------------
> +;
> +; Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
> +; SPDX-License-Identifier: BSD-2-Clause-Patent
> +;
> +; Module Name:
> +;
> +;   VmgExit.Asm
> +;
> +; Abstract:
> +;
> +;   AsmVmgExit function
> +;
> +; Notes:
> +;
> +;------------------------------------------------------------------------------
> +
> +    SECTION .text
> +
> +;------------------------------------------------------------------------------
> +; VOID
> +; EFIAPI
> +; AsmVmgExit (
> +;   VOID
> +;   );
> +;------------------------------------------------------------------------------
> +global ASM_PFX(AsmVmgExit)
> +ASM_PFX(AsmVmgExit):
> +;
> +; NASM doesn't support the vmmcall instruction in 32-bit mode and NASM versions
> +; before 2.12 cannot translate the 64-bit "rep vmmcall" instruction into elf32
> +; format. Given that VMGEXIT does not make sense on IA32, provide a stub
> +; implementation that is identical to CpuBreakpoint(). In practice, AsmVmgExit()
> +; should never be called on IA32.
> +;
> +    int  3
> +    ret
> +
> diff --git a/MdePkg/Library/BaseLib/X64/VmgExit.nasm b/MdePkg/Library/BaseLib/X64/VmgExit.nasm
> new file mode 100644
> index 000000000000..26f034593c67
> --- /dev/null
> +++ b/MdePkg/Library/BaseLib/X64/VmgExit.nasm
> @@ -0,0 +1,32 @@
> +;------------------------------------------------------------------------------
> +;
> +; Copyright (C) 2020, Advanced Micro Devices, Inc. All rights reserved.<BR>
> +; SPDX-License-Identifier: BSD-2-Clause-Patent
> +;
> +; Module Name:
> +;
> +;   VmgExit.Asm
> +;
> +; Abstract:
> +;
> +;   AsmVmgExit function
> +;
> +; Notes:
> +;
> +;------------------------------------------------------------------------------
> +
> +    DEFAULT REL
> +    SECTION .text
> +
> +;------------------------------------------------------------------------------
> +; VOID
> +; EFIAPI
> +; AsmVmgExit (
> +;   VOID
> +;   );
> +;------------------------------------------------------------------------------
> +global ASM_PFX(AsmVmgExit)
> +ASM_PFX(AsmVmgExit):
> +    rep     vmmcall
> +    ret
> +
> 

FWIW:

Reviewed-by: Laszlo Ersek <lersek@redhat.com>