[PATCH v8 34/46] OvmfPkg: Reserve a page in memory for the SEV-ES usage

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

Reserve a fixed area of memory for SEV-ES use and set a fixed PCD,
PcdSevEsWorkAreaBase, to this value.

This area will be used by SEV-ES support for two purposes:
  1. Communicating the SEV-ES status during BSP boot to SEC:
     Using a byte of memory from the page, the BSP reset vector code can
     communicate the SEV-ES status to SEC for use before exception
     handling can be enabled in SEC. After SEC, this field is no longer
     valid and the standard way of determine if SEV-ES is active should
     be used.

  2. Establishing an area of memory for AP boot support:
     A hypervisor is not allowed to update an SEV-ES guest's register
     state, so when booting an SEV-ES guest AP, the hypervisor is not
     allowed to set the RIP to the guest requested value. Instead an
     SEV-ES AP must be re-directed from within the guest to the actual
     requested staring location as specified in the INIT-SIPI-SIPI
     sequence.

     Use this memory for reset vector code that can be programmed to have
     the AP jump to the desired RIP location after starting the AP. This
     is required for only the very first AP reset.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 OvmfPkg/OvmfPkgX64.fdf                    |  3 +++
 OvmfPkg/ResetVector/ResetVector.inf       |  1 +
 OvmfPkg/ResetVector/Ia32/PageTables64.asm | 11 +++++++++++
 OvmfPkg/ResetVector/ResetVector.nasmb     |  1 +
 4 files changed, 16 insertions(+)

diff --git a/OvmfPkg/OvmfPkgX64.fdf b/OvmfPkg/OvmfPkgX64.fdf
index 88b1e880e603..8836b30a0cef 100644
--- a/OvmfPkg/OvmfPkgX64.fdf
+++ b/OvmfPkg/OvmfPkgX64.fdf
@@ -82,6 +82,9 @@ [FD.MEMFD]
 0x009000|0x002000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize
 
+0x00B000|0x001000
+gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase|gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaSize
+
 0x010000|0x010000
 gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecPeiTempRamSize
 
diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/ResetVector.inf
index 483fd90fe785..e94e1bfcce7e 100644
--- a/OvmfPkg/ResetVector/ResetVector.inf
+++ b/OvmfPkg/ResetVector/ResetVector.inf
@@ -34,6 +34,7 @@ [BuildOptions]
    *_*_X64_NASMB_FLAGS = -I$(WORKSPACE)/UefiCpuPkg/ResetVector/Vtf0/
 
 [Pcd]
+  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBase
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbSize
   gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbPageTableBase
diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
index c3587a1b7814..73a4eaadb1b6 100644
--- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
+++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
@@ -89,6 +89,10 @@ SevExit:
 ; If SEV-ES is disabled then EAX will be zero.
 ;
 CheckSevEsFeature:
+    ; Initialize the first byte of the workarea to zero to communicate to
+    ; the SEC phase that SEV-ES is not enabled.
+    mov     byte[SEV_ES_WORK_AREA], 0
+
     xor       eax, eax
 
     ; SEV-ES can't be enabled if SEV isn't, so first check the encryption
@@ -108,6 +112,13 @@ CheckSevEsFeature:
     ; Restore encryption mask
     mov       edx, ebx
 
+    test      eax, eax
+    jz        NoSevEs
+
+    ; Set the first byte of the workarea to one to communicate to the SEC
+    ; phase that SEV-ES is enabled.
+    mov       byte[SEV_ES_WORK_AREA], 1
+
 NoSevEs:
     OneTimeCallRet CheckSevEsFeature
 
diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
index bfb77e439105..2967617bfaa0 100644
--- a/OvmfPkg/ResetVector/ResetVector.nasmb
+++ b/OvmfPkg/ResetVector/ResetVector.nasmb
@@ -72,6 +72,7 @@
   %define GHCB_PT_ADDR (FixedPcdGet32 (PcdOvmfSecGhcbPageTableBase))
   %define GHCB_BASE (FixedPcdGet32 (PcdOvmfSecGhcbBase))
   %define GHCB_SIZE (FixedPcdGet32 (PcdOvmfSecGhcbSize))
+  %define SEV_ES_WORK_AREA (FixedPcdGet32 (PcdSevEsWorkAreaBase))
 %include "Ia32/PageTables64.asm"
 %endif
 
-- 
2.17.1