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Date: Fri, 20 Aug 2021 08:41:15 +0200
From: "Gerd Hoffmann" <kraxel@redhat.com>
To: "Xu, Min M" <min.m.xu@intel.com>
Cc: "devel@edk2.groups.io" <devel@edk2.groups.io>,
	"Kinney, Michael D" <michael.d.kinney@intel.com>,
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	"Yao, Jiewen" <jiewen.yao@intel.com>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [edk2-devel] [PATCH 07/23] MdePkg: Update BaseIoLibIntrinsicSev to support Tdx
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  Hi,

> > One more question:  How does this align with the WorkArea changes posted
> > yesterday?  The WorkArea gets a mode field for SEV / TDX / normal, so I think
> > you should be able to use that instead of invoking cpuid each time you need
> > to know whenever tdx is active or not.
> We don't want to make the TdxProbeLib depend on the WorkArea.

Why?

> CPUID(0x21) makes TdxProbeLib less dependency.  For Intel TDX the
> WorkArea is designed to be used in ResetVector phase.

I don't see why the dependency is a problem.  TDX-enabled builds need
both TdxProbeLib / TdxLib and WorkArea anyway.

Each cpuid instruction is a vmexit, and the code invokes cpuid twice for
each io / mmio access.

take care,
  Gerd