[PATCH v6 24/29] UefiCpuPkg/MpInitLib: use BSP to do extended topology check

["Brijesh Singh" <brijesh.singh@amd.com>]

From: Michael Roth <michael.roth@amd.com>

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>
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/MpLib.h          |  1 +
 UefiCpuPkg/Library/MpInitLib/MpLib.c          | 11 ++++++++
 UefiCpuPkg/Library/MpInitLib/MpEqu.inc        |  1 +
 UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm | 27 +++++++++++++++++++
 4 files changed, 40 insertions(+)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h b/UefiCpuPkg/Library/MpInitLib/MpLib.h
index 4abaa2243d0a..19e91bf7d74e 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
@@ -220,6 +220,7 @@ typedef struct {
   BOOLEAN               SevEsIsEnabled;
   BOOLEAN               SevSnpIsEnabled;
   UINTN                 GhcbBase;
+  BOOLEAN               ExtTopoAvail;
 } MP_CPU_EXCHANGE_INFO;
 
 #pragma pack()
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index 586cff2f6813..c2b00a1f04ff 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -1004,6 +1004,7 @@ FillExchangeInfoData (
   UINTN                            Size;
   IA32_SEGMENT_DESCRIPTOR          *Selector;
   IA32_CR4                         Cr4;
+  UINT32                           StdRangeMax;
 
   ExchangeInfo                  = CpuMpData->MpCpuExchangeInfo;
   ExchangeInfo->StackStart      = CpuMpData->Buffer;
@@ -1043,6 +1044,16 @@ FillExchangeInfoData (
   ExchangeInfo->SevSnpIsEnabled = CpuMpData->SevSnpIsEnabled;
   ExchangeInfo->GhcbBase        = (UINTN) CpuMpData->GhcbBase;
 
+  if (ExchangeInfo->SevSnpIsEnabled) {
+    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;
+    }
+  }
+
   //
   // Get the BSP's data of GDT and IDT
   //
diff --git a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc b/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
index 01668638f245..aba53f57201c 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpEqu.inc
+++ b/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)
diff --git a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
index 19939c093d2e..76d07a275c7b 100644
--- a/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm
@@ -264,6 +264,32 @@ GetApicId:
     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
@@ -282,6 +308,7 @@ GetApicId:
     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
-- 
2.17.1