UefiCpuPkg/MpInitLib: use BSP to do extended topology check

During AP bringup, just after switching to long mode, APs will do some
cpuid calls to verify that the extended topology leaf (0xB) is available
so they can fetch their x2 APIC IDs from it. In the case of SEV-ES,
these cpuid instructions must be handled by direct use of the GHCB MSR
protocol to fetch the values from the hypervisor, since a #VC handler
is not yet available due to the AP's stack not being set up yet.

For SEV-SNP, rather than relying on the GHCB MSR protocol, it is
expected that these values would be obtained from the SEV-SNP CPUID
table instead. The actual x2 APIC ID (and 8-bit APIC IDs) would still
be fetched from hypervisor using the GHCB MSR protocol however, so
introducing support for the SEV-SNP CPUID table in that part of the AP
bring-up code would only be to handle the checks/validation of the
extended topology leaf.

Rather than introducing all the added complexity needed to handle these
checks via the CPUID table, instead let the BSP do the check in advance,
since it can make use of the #VC handler to avoid the need to scan the
SNP CPUID table directly, and add a flag in ExchangeInfo to communicate
the result of this check to APs.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Rahul Kumar <rahul1.kumar@intel.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Min Xu <min.m.xu@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Ray Ni <ray.ni@intel.com>
Suggested-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>

UefiCpuPkg/Library/MpInitLib/AmdSev.c

@@ -243,3 +243,24 @@ SevEsPlaceApHlt (
 
   MpInitLibSevEsAPReset (Ghcb, CpuMpData);
 }
+
+/**
+  The function fills the exchange data for the AP.
+
+  @param[in]   ExchangeInfo  The pointer to CPU Exchange Data structure
+**/
+VOID
+FillExchangeInfoDataSevEs (
+  IN volatile MP_CPU_EXCHANGE_INFO  *ExchangeInfo
+  )
+{
+  UINT32  StdRangeMax;
+
+  AsmCpuid (CPUID_SIGNATURE, &StdRangeMax, NULL, NULL, NULL);
+  if (StdRangeMax >= CPUID_EXTENDED_TOPOLOGY) {
+    CPUID_EXTENDED_TOPOLOGY_EBX  ExtTopoEbx;
+
+    AsmCpuid (CPUID_EXTENDED_TOPOLOGY, NULL, &ExtTopoEbx.Uint32, NULL, NULL);
+    ExchangeInfo->ExtTopoAvail = !!ExtTopoEbx.Bits.LogicalProcessors;
+  }
+}

UefiCpuPkg/Library/MpInitLib/MpEqu.inc

@@ -94,6 +94,7 @@ struc MP_CPU_EXCHANGE_INFO
   .SevEsIsEnabled:               CTYPE_BOOLEAN 1
   .SevSnpIsEnabled               CTYPE_BOOLEAN 1
   .GhcbBase:                     CTYPE_UINTN 1
+  .ExtTopoAvail:                 CTYPE_BOOLEAN 1
 endstruc
 
 MP_CPU_EXCHANGE_INFO_OFFSET equ (SwitchToRealProcEnd - RendezvousFunnelProcStart)

UefiCpuPkg/Library/MpInitLib/MpLib.c

@@ -900,6 +900,13 @@ FillExchangeInfoData (
   ExchangeInfo->SevSnpIsEnabled = CpuMpData->SevSnpIsEnabled;
   ExchangeInfo->GhcbBase        = (UINTN)CpuMpData->GhcbBase;
 
+  //
+  // Populate SEV-ES specific exchange data.
+  //
+  if (ExchangeInfo->SevSnpIsEnabled) {
+    FillExchangeInfoDataSevEs (ExchangeInfo);
+  }
+
   //
   // Get the BSP's data of GDT and IDT
   //

UefiCpuPkg/Library/MpInitLib/MpLib.h

@@ -224,6 +224,7 @@ typedef struct {
   BOOLEAN            SevEsIsEnabled;
   BOOLEAN            SevSnpIsEnabled;
   UINTN              GhcbBase;
+  BOOLEAN            ExtTopoAvail;
 } MP_CPU_EXCHANGE_INFO;
 
 #pragma pack()
@@ -788,4 +789,14 @@ ConfidentialComputingGuestHas (
   CONFIDENTIAL_COMPUTING_GUEST_ATTR  Attr
   );
 
+/**
+  The function fills the exchange data for the AP.
+
+  @param[in]   ExchangeInfo  The pointer to CPU Exchange Data structure
+**/
+VOID
+FillExchangeInfoDataSevEs (
+  IN volatile MP_CPU_EXCHANGE_INFO  *ExchangeInfo
+  );
+
 #endif

UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm

@@ -118,6 +118,32 @@ SevEsGetApicId:
     or         rax, rdx
     mov        rdi, rax             ; RDI now holds the original GHCB GPA
 
+    ;
+    ; For SEV-SNP, the recommended handling for getting the x2APIC ID
+    ; would be to use the SNP CPUID table to fetch CPUID.00H:EAX and
+    ; CPUID:0BH:EBX[15:0] instead of the GHCB MSR protocol vmgexits
+    ; below.
+    ;
+    ; To avoid the unecessary ugliness to accomplish that here, the BSP
+    ; has performed these checks in advance (where #VC handler handles
+    ; the CPUID table lookups automatically) and cached them in a flag
+    ; so those checks can be skipped here.
+    ;
+    mov        eax, [esi + MP_CPU_EXCHANGE_INFO_FIELD (SevSnpIsEnabled)]
+    cmp        al, 1
+    jne        CheckExtTopoAvail
+
+    ;
+    ; Even with SEV-SNP, the actual x2APIC ID in CPUID.0BH:EDX
+    ; fetched from the hypervisor the same way SEV-ES does it.
+    ;
+    mov        eax, [esi + MP_CPU_EXCHANGE_INFO_FIELD (ExtTopoAvail)]
+    cmp        al, 1
+    je         GetApicIdSevEs
+    ; The 8-bit APIC ID fallback is also the same as with SEV-ES
+    jmp        NoX2ApicSevEs
+
+CheckExtTopoAvail:
     mov        rdx, 0               ; CPUID function 0
     mov        rax, 0               ; RAX register requested
     or         rax, 4
@@ -136,6 +162,7 @@ SevEsGetApicId:
     test       edx, 0ffffh
     jz         NoX2ApicSevEs        ; CPUID.0BH:EBX[15:0] is zero
 
+GetApicIdSevEs:
     mov        rdx, 0bh             ; CPUID function 0x0b
     mov        rax, 0c0000000h      ; RDX register requested
     or         rax, 4