UefiCpuPkg/DxeMpInitLib: Add a PCD to allow the AP wakeup buffer to be reserved

[kenlautner]

Description

Creates a new PCD which when set will cause the AP wakeup buffer to be allocated as a reserved type.

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• Breaking change?
  • Breaking change - Does this PR cause a break in build or boot behavior?
  • Examples: Does it add a new library class or move a module to a different repo.
• Impacts security?
  • Security - Does this PR have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• Includes tests?
  • Tests - Does this PR include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Tested on custom Q35 image

Integration Instructions

N/A

[niruiyu]

There is an existing path for reserved memory allocation.
Why do you need a new path?

[kenlautner]

The other path for the AP wakeup buffer to be reserved requires specific confidential computing attributes to be set. This allows you to just have the AP wakeup buffer be reserved through a PCD if you need it.

[niruiyu]

The other path for the AP wakeup buffer to be reserved requires specific confidential computing attributes to be set. This allows you to just have the AP wakeup buffer be reserved through a PCD if you need it.

Can you unify the two paths into one?

[kenlautner]

The other path for the AP wakeup buffer to be reserved requires specific confidential computing attributes to be set. This allows you to just have the AP wakeup buffer be reserved through a PCD if you need it.

Can you unify the two paths into one?

Sure. Would this be acceptable?

if ((PcdGetBool (PcdCpuApWakeupBufferReserved)) || 
     (ConfidentialComputingGuestHas (CCAttrAmdSevEs) &&
     !ConfidentialComputingGuestHas (CCAttrAmdSevSnp))) {
    MemoryType = EfiReservedMemoryType;
 }

[github-actions]

This PR has been automatically marked as stale because it has not had activity in 60 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions.

[kenlautner]

The other path for the AP wakeup buffer to be reserved requires specific confidential computing attributes to be set. This allows you to just have the AP wakeup buffer be reserved through a PCD if you need it.

Can you unify the two paths into one?

Sure. Would this be acceptable?

if ((PcdGetBool (PcdCpuApWakeupBufferReserved)) || 
     (ConfidentialComputingGuestHas (CCAttrAmdSevEs) &&
     !ConfidentialComputingGuestHas (CCAttrAmdSevSnp))) {
    MemoryType = EfiReservedMemoryType;
 }

@niruiyu bumping the original comment.