[edk2-devel] [PATCH v2 1/1] UefiCpuPkg/MpInitLib: Reduce reset vector memory pressure

[Lendacky, Thomas]

From: Tom Lendacky <thomas.lendacky at amd.com>

The AP reset vector stack allocation is only required if running as an
SEV-ES guest. Since the reset vector allocation is below 1MB in memory,
eliminate the requirement for bare-metal systems and non SEV-ES guests
to allocate the extra stack area, which can be large if the
PcdCpuMaxLogicalProcessorNumber value is large, and also remove the
CPU_STACK_ALIGNMENT alignment.

Fixes: 7b7508ad784d ("UefiCpuPkg: Allow AP booting under SEV-ES")
Cc: Garrett Kirkendall <garrett.kirkendall at amd.com>
Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
---
 UefiCpuPkg/Library/MpInitLib/MpLib.c | 36 +++++++++-----------
 1 file changed, 17 insertions(+), 19 deletions(-)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 07426274f639..a9708c6479d2 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1141,20 +1141,6 @@ RestoreWakeupBuffer(
     );
 }
 
-/**
-  Calculate the size of the reset stack.
-
-  @return                 Total amount of memory required for stacks
-**/
-STATIC
-UINTN
-GetApResetStackSize (
-  VOID
-  )
-{
-  return AP_RESET_STACK_SIZE * PcdGet32(PcdCpuMaxLogicalProcessorNumber);
-}
-
 /**
   Calculate the size of the reset vector.
 
@@ -1170,11 +1156,23 @@ GetApResetVectorSize (
 {
   UINTN  Size;
 
-  Size = ALIGN_VALUE (AddressMap->RendezvousFunnelSize +
-                        AddressMap->SwitchToRealSize +
-                        sizeof (MP_CPU_EXCHANGE_INFO),
-                      CPU_STACK_ALIGNMENT);
-  Size += GetApResetStackSize ();
+  Size = AddressMap->RendezvousFunnelSize +
+           AddressMap->SwitchToRealSize +
+           sizeof (MP_CPU_EXCHANGE_INFO);
+
+  //
+  // The AP reset stack is only used by SEV-ES guests. Do not add to the
+  // allocation if SEV-ES is not enabled.
+  //
+  if (PcdGetBool (PcdSevEsIsEnabled)) {
+    //
+    // Stack location is based on APIC ID, so use the total number of
+    // processors for calculating the total stack area.
+    //
+    Size += AP_RESET_STACK_SIZE * PcdGet32(PcdCpuMaxLogicalProcessorNumber);
+
+    Size = ALIGN_VALUE (Size, CPU_STACK_ALIGNMENT);
+  }
 
   return Size;
 }
-- 
2.28.0



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