Re: [edk2-devel] [Patch V2 1/6] MdePkg: Add PcdSpeculationBarrierType

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

On 04/30/19 03:30, Michael D Kinney wrote:
> Add gEfiMdePkgTokenSpaceGuid.PcdSpeculationBarrierType that
> uses the PCD type FixedAtBuild.  This performs a build time
> selection for the type of speculation barrier to use in the
> BaseLib function SpeculationBarrier().  The recommended
> speculation barrier for x86 is LFENCE and this is the default
> value for this PCD.  x86 CPUs that do not support LFENCE must
> select one of the other supported values which includes CPUID
> and nothing.
> 
> Cc: Liming Gao <liming.gao@intel.com>
> Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
> ---
>  MdePkg/MdePkg.dec | 9 +++++++++
>  MdePkg/MdePkg.uni | 8 ++++++++
>  2 files changed, 17 insertions(+)
> 
> diff --git a/MdePkg/MdePkg.dec b/MdePkg/MdePkg.dec
> index e2ea8fff66..28d4a966c2 100644
> --- a/MdePkg/MdePkg.dec
> +++ b/MdePkg/MdePkg.dec
> @@ -2062,6 +2062,15 @@ [PcdsFixedAtBuild]
>    # @Prompt Enable control flow enforcement.
>    gEfiMdePkgTokenSpaceGuid.PcdControlFlowEnforcementPropertyMask|0x0|UINT32|0x30001017
>  
> +  ## Indicates the type of instruction sequence to use for a speculation
> +  #  barrier.  The default instruction sequence is LFENCE.<BR><BR>
> +  #   0x00 - No operation.<BR>
> +  #   0x01 - LFENCE (IA32/X64).<BR>
> +  #   0x02 - CPUID  (IA32/X64).<BR>
> +  #   Other - reserved
> +  # @Prompt Speculation Barrier Type.
> +  gEfiMdePkgTokenSpaceGuid.PcdSpeculationBarrierType|0x01|UINT8|0x30001018
> +
>  [PcdsFixedAtBuild,PcdsPatchableInModule]
>    ## Indicates the maximum length of unicode string used in the following
>    #  BaseLib functions: StrLen(), StrSize(), StrCmp(), StrnCmp(), StrCpy(), StrnCpy()<BR><BR>

In MdePkg.dec, we have:
- [Includes.X64]
- [LibraryClasses.X64]
- [Guids.X64]

but no PCD declarations that are architecture-specific. Is that
intentional? Because, this PCD could be a good candidate for "IA32/X64
only". (Looking at the next patch too.)

But, that's just my curiosity.

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

Thanks
Laszlo


> diff --git a/MdePkg/MdePkg.uni b/MdePkg/MdePkg.uni
> index c359bb4b5b..5c1fa24065 100644
> --- a/MdePkg/MdePkg.uni
> +++ b/MdePkg/MdePkg.uni
> @@ -149,6 +149,14 @@
>                                                                                                    " BIT0 - SMM CET Shadow Stack is enabled.<BR>\n"
>                                                                                                    " Other - reserved"
>  
> +#string STR_gEfiMdePkgTokenSpaceGuid_PcdSpeculationBarrierType_PROMPT  #language en-US "Speculation Barrier Type."
> +
> +#string STR_gEfiMdePkgTokenSpaceGuid_PcdSpeculationBarrierType_HELP  #language en-US  "Indicates the type of instruction sequence to use for a speculation.barrier.  The default instruction sequence is LFENCE.<BR><BR>\n"
> +                                                                                      "0x00 - No operation.<BR>\n"
> +                                                                                      "0x01 - LFENCE (IA32/X64).<BR>\n"
> +                                                                                      "0x02 - CPUID  (IA32/X64).<BR>\n"
> +                                                                                      "Other - reserved"
> +
>  #string STR_gEfiMdePkgTokenSpaceGuid_PcdMaximumAsciiStringLength_PROMPT  #language en-US "Maximum Length of Ascii String"
>  
>  #string STR_gEfiMdePkgTokenSpaceGuid_PcdMaximumAsciiStringLength_HELP  #language en-US "Sets the maximum number of ASCII characters used for string functions.  This affects the following BaseLib functions: AsciiStrLen(), AsciiStrSize(), AsciiStrCmp(), AsciiStrnCmp(), AsciiStrCpy(), AsciiStrnCpy(). <BR><BR>\n"
>