[PATCH v10 27/32] UefiCpuPkg/MpInitLib: use BSP to do extended topology check

Brijesh Singh

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>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.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/AmdSev.nasm | 27 ++++++++++++++++++++
4 files changed, 40 insertions(+)

diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.h b/UefiCpuPkg/Library/MpInitLib/MpLib.h
index 45bc1de23e3c..c52b6157429b 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.h
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.h
@@ -224,6 +224,7 @@ typedef struct {
BOOLEAN SevEsIsEnabled;
BOOLEAN SevSnpIsEnabled;
UINTN GhcbBase;
+ BOOLEAN ExtTopoAvail;

#pragma pack()
diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
index b05eb4413a95..9a9d9100d543 100644
--- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
+++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
@@ -853,6 +853,7 @@ FillExchangeInfoData (
IA32_CR4 Cr4;
+ UINT32 StdRangeMax;

ExchangeInfo = CpuMpData->MpCpuExchangeInfo;
ExchangeInfo->StackStart = CpuMpData->Buffer;
@@ -892,6 +893,16 @@ FillExchangeInfoData (
ExchangeInfo->SevSnpIsEnabled = CpuMpData->SevSnpIsEnabled;
ExchangeInfo->GhcbBase = (UINTN) CpuMpData->GhcbBase;

+ if (ExchangeInfo->SevSnpIsEnabled) {
+ 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

MP_CPU_EXCHANGE_INFO_OFFSET equ (SwitchToRealProcEnd - RendezvousFunnelProcStart)
diff --git a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm b/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm
index 0034920b2f6b..8bb1161fa0f7 100644
--- a/UefiCpuPkg/Library/MpInitLib/X64/AmdSev.nasm
+++ b/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
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

mov rdx, 0bh ; CPUID function 0x0b
mov rax, 0c0000000h ; RDX register requested
or rax, 4

Join devel@edk2.groups.io to automatically receive all group messages.