UefiCpuPkg:Wake up APs after power-up or RESET through SIPI.

The implementation of this new behavior aligns with the guidelines
outlined in the Intel SDM.

Following a power-up or RESET of an MP system, system hardware
dynamically selects one of the processors on the system bus as the BSP.
The remaining processors are designated as APs. The APs complete a
minimal self-configuration, then wait for a startup signal (a SIPI
message) from the BSP processor.

Additionally, the MP protocol is executed only after
a power-up or RESET. If the MP protocol has completed and a
BSP is chosen, subsequent INITs (either to a specific processor or
system wide) do not cause the MP protocol to be repeated. Instead, each
logical processor examines its BSP flag (in the IA32_APIC_BASE MSR) to
determine whether it should execute the BIOS boot-strap code (if it is
the BSP) or enter a wait-for-SIPI state (if it is an AP).

Cc: Eric Dong <[email protected]>
Cc: Ray Ni <[email protected]>
Cc: Rahul Kumar <[email protected]>
Cc: Gerd Hoffmann <[email protected]>
Signed-off-by: Ray Ni <[email protected]>
Signed-off-by: Yuanhao Xie <[email protected]>
Reviewed-by: Ray Ni <[email protected]>

UefiCpuPkg/Library/MpInitLib/MpLib.c

@@ -1294,7 +1294,14 @@ WakeUpAP (
       if (CpuMpData->SevSnpIsEnabled && (CpuMpData->InitFlag != ApInitConfig)) {
         SevSnpCreateAP (CpuMpData, -1);
       } else {
-        SendInitSipiSipiAllExcludingSelf ((UINT32)ExchangeInfo->BufferStart);
+        if ((CpuMpData->InitFlag == ApInitConfig) && FixedPcdGetBool (PcdFirstTimeWakeUpAPsBySipi)) {
+          //
+          // SIPI can be used for the first time wake up after reset to reduce boot time.
+          //
+          SendStartupIpiAllExcludingSelf ((UINT32)ExchangeInfo->BufferStart);
+        } else {
+          SendInitSipiSipiAllExcludingSelf ((UINT32)ExchangeInfo->BufferStart);
+        }
       }
     }