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Subject: Re: [edk2-devel] [Patch V2 2/6] MdePkg/BaseLib: Use PcdSpeculationBarrierType
To: devel@edk2.groups.io, michael.d.kinney@intel.com
Cc: Liming Gao <liming.gao@intel.com>
References: <20190430013012.24008-1-michael.d.kinney@intel.com>
 <20190430013012.24008-3-michael.d.kinney@intel.com>
From: "Laszlo Ersek" <lersek@redhat.com>
Message-ID: <14c3be99-8187-39ab-2293-bc7aaa6b0abe@redhat.com>
Date: Tue, 30 Apr 2019 13:49:45 +0200
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On 04/30/19 03:30, Michael D Kinney wrote:
> Use PcdSpeculationBarrierType in the x86 implementation
> of SpeculationBarrier() to select between AsmLfence(),
> AsmCpuid(), and no operation.
> 
> Cc: Liming Gao <liming.gao@intel.com>
> Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
> ---
>  MdePkg/Library/BaseLib/BaseLib.inf             | 1 +
>  MdePkg/Library/BaseLib/X86SpeculationBarrier.c | 8 ++++++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf b/MdePkg/Library/BaseLib/BaseLib.inf
> index 533e83e0b2..3586beb0ab 100644
> --- a/MdePkg/Library/BaseLib/BaseLib.inf
> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> @@ -394,6 +394,7 @@ [Pcd]
>    gEfiMdePkgTokenSpaceGuid.PcdMaximumAsciiStringLength     ## SOMETIMES_CONSUMES
>    gEfiMdePkgTokenSpaceGuid.PcdMaximumUnicodeStringLength   ## SOMETIMES_CONSUMES
>    gEfiMdePkgTokenSpaceGuid.PcdControlFlowEnforcementPropertyMask   ## SOMETIMES_CONSUMES
> +  gEfiMdePkgTokenSpaceGuid.PcdSpeculationBarrierType       ## SOMETIMES_CONSUMES
>  
>  [FeaturePcd]
>    gEfiMdePkgTokenSpaceGuid.PcdVerifyNodeInList  ## CONSUMES

So, based on the example of

  MdePkg/Library/SecPeiDxeTimerLibCpu/SecPeiDxeTimerLibCpu.inf

and a few other INF files, I think we could use

  [Pcd.IA32, Pcd.X64]

here as well.

Just an idea.

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

Thanks
Laszlo

> diff --git a/MdePkg/Library/BaseLib/X86SpeculationBarrier.c b/MdePkg/Library/BaseLib/X86SpeculationBarrier.c
> index 8e5f983bb8..b28fd8de9b 100644
> --- a/MdePkg/Library/BaseLib/X86SpeculationBarrier.c
> +++ b/MdePkg/Library/BaseLib/X86SpeculationBarrier.c
> @@ -1,7 +1,7 @@
>  /** @file
>    SpeculationBarrier() function for IA32 and x64.
>  
> -  Copyright (C) 2018, Intel Corporation. All rights reserved.<BR>
> +  Copyright (C) 2018 - 2019, Intel Corporation. All rights reserved.<BR>
>  
>    SPDX-License-Identifier: BSD-2-Clause-Patent
>  
> @@ -22,5 +22,9 @@ SpeculationBarrier (
>    VOID
>    )
>  {
> -  AsmLfence ();
> +  if (PcdGet8 (PcdSpeculationBarrierType) == 0x01) {
> +    AsmLfence ();
> +  } else if (PcdGet8 (PcdSpeculationBarrierType) == 0x02) {
> +    AsmCpuid (0x01, NULL, NULL, NULL, NULL);
> +  }
>  }
>