UefiCpuPkg/MpInitLib: use BSP to do extended topology check

[mirror_edk2.git] / UefiCpuPkg / Library / MpInitLib / X64 / AmdSev.nasm

diff --git a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm b/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm
index 0034920b2f6b1785e359b95c2e6a5865668b7fc0..8bb1161fa0f77fe4681eaa872e7e8dd844ebf80a 100644 (file)
--- a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm
+++ b/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm
@@ -118,6 +118,32 @@ SevEsGetApicId:
     or         rax, rdx\r
     mov        rdi, rax             ; RDI now holds the original GHCB GPA\r
 \r
+    ;\r
+    ; For SEV-SNP, the recommended handling for getting the x2APIC ID\r
+    ; would be to use the SNP CPUID table to fetch CPUID.00H:EAX and\r
+    ; CPUID:0BH:EBX[15:0] instead of the GHCB MSR protocol vmgexits\r
+    ; below.\r
+    ;\r
+    ; To avoid the unecessary ugliness to accomplish that here, the BSP\r
+    ; has performed these checks in advance (where #VC handler handles\r
+    ; the CPUID table lookups automatically) and cached them in a flag\r
+    ; so those checks can be skipped here.\r
+    ;\r
+    mov        eax, [esi + MP_CPU_EXCHANGE_INFO_FIELD (SevSnpIsEnabled)]\r
+    cmp        al, 1\r
+    jne        CheckExtTopoAvail\r
+\r
+    ;\r
+    ; Even with SEV-SNP, the actual x2APIC ID in CPUID.0BH:EDX\r
+    ; fetched from the hypervisor the same way SEV-ES does it.\r
+    ;\r
+    mov        eax, [esi + MP_CPU_EXCHANGE_INFO_FIELD (ExtTopoAvail)]\r
+    cmp        al, 1\r
+    je         GetApicIdSevEs\r
+    ; The 8-bit APIC ID fallback is also the same as with SEV-ES\r
+    jmp        NoX2ApicSevEs\r
+\r
+CheckExtTopoAvail:\r
     mov        rdx, 0               ; CPUID function 0\r
     mov        rax, 0               ; RAX register requested\r
     or         rax, 4\r
@@ -136,6 +162,7 @@ SevEsGetApicId:
     test       edx, 0ffffh\r
     jz         NoX2ApicSevEs        ; CPUID.0BH:EBX[15:0] is zero\r
 \r
+GetApicIdSevEs:\r
     mov        rdx, 0bh             ; CPUID function 0x0b\r
     mov        rax, 0c0000000h      ; RDX register requested\r
     or         rax, 4\r