[PATCH v3 3/3] OvmfPkg/ResetVector: move the GHCB page setup in AmdSev.asm

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

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3429

While build the initial page table, the SetCr3ForPageTables64 checks
whether SEV-ES is enabled. If so, clear the page encryption mask from the
GHCB page. Move the logic to clear the page encryption mask in the
AmdSev.asm.

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>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 OvmfPkg/ResetVector/Ia32/AmdSev.asm       | 111 +++++++++++++++++-----
 OvmfPkg/ResetVector/Ia32/PageTables64.asm |  53 ++---------
 2 files changed, 92 insertions(+), 72 deletions(-)

diff --git a/OvmfPkg/ResetVector/Ia32/AmdSev.asm b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
index 87d81b01e263..250ac8d8b180 100644
--- a/OvmfPkg/ResetVector/Ia32/AmdSev.asm
+++ b/OvmfPkg/ResetVector/Ia32/AmdSev.asm
@@ -44,6 +44,27 @@ BITS    32
 ; The unexpected response code
 %define TERM_UNEXPECTED_RESP_CODE   2
 
+%define PAGE_PRESENT            0x01
+%define PAGE_READ_WRITE         0x02
+%define PAGE_USER_SUPERVISOR    0x04
+%define PAGE_WRITE_THROUGH      0x08
+%define PAGE_CACHE_DISABLE     0x010
+%define PAGE_ACCESSED          0x020
+%define PAGE_DIRTY             0x040
+%define PAGE_PAT               0x080
+%define PAGE_GLOBAL           0x0100
+%define PAGE_2M_MBO            0x080
+%define PAGE_2M_PAT          0x01000
+
+%define PAGE_4K_PDE_ATTR (PAGE_ACCESSED + \
+                          PAGE_DIRTY + \
+                          PAGE_READ_WRITE + \
+                          PAGE_PRESENT)
+
+%define PAGE_PDP_ATTR (PAGE_ACCESSED + \
+                       PAGE_READ_WRITE + \
+                       PAGE_PRESENT)
+
 
 ; Macro is used to issue the MSR protocol based VMGEXIT. The caller is
 ; responsible to populate values in the EDX:EAX registers. After the vmmcall
@@ -117,6 +138,70 @@ BITS    32
 SevEsUnexpectedRespTerminate:
     TerminateVmgExit    TERM_UNEXPECTED_RESP_CODE
 
+; If SEV-ES is enabled then initialize and make the GHCB page shared
+SevClearPageEncMaskForGhcbPage:
+    ; Check if SEV is enabled
+    cmp       byte[WORK_AREA_GUEST_TYPE], 1
+    jnz       SevClearPageEncMaskForGhcbPageExit
+
+    ; Check if SEV-ES is enabled
+    cmp       byte[SEV_ES_WORK_AREA], 1
+    jnz       SevClearPageEncMaskForGhcbPageExit
+
+    ;
+    ; The initial GHCB will live at GHCB_BASE and needs to be un-encrypted.
+    ; This requires the 2MB page for this range be broken down into 512 4KB
+    ; pages.  All will be marked encrypted, except for the GHCB.
+    ;
+    mov     ecx, (GHCB_BASE >> 21)
+    mov     eax, GHCB_PT_ADDR + PAGE_PDP_ATTR
+    mov     [ecx * 8 + PT_ADDR (0x2000)], eax
+
+    ;
+    ; Page Table Entries (512 * 4KB entries => 2MB)
+    ;
+    mov     ecx, 512
+pageTableEntries4kLoop:
+    mov     eax, ecx
+    dec     eax
+    shl     eax, 12
+    add     eax, GHCB_BASE & 0xFFE0_0000
+    add     eax, PAGE_4K_PDE_ATTR
+    mov     [ecx * 8 + GHCB_PT_ADDR - 8], eax
+    mov     [(ecx * 8 + GHCB_PT_ADDR - 8) + 4], edx
+    loop    pageTableEntries4kLoop
+
+    ;
+    ; Clear the encryption bit from the GHCB entry
+    ;
+    mov     ecx, (GHCB_BASE & 0x1F_FFFF) >> 12
+    mov     [ecx * 8 + GHCB_PT_ADDR + 4], strict dword 0
+
+    mov     ecx, GHCB_SIZE / 4
+    xor     eax, eax
+clearGhcbMemoryLoop:
+    mov     dword[ecx * 4 + GHCB_BASE - 4], eax
+    loop    clearGhcbMemoryLoop
+
+SevClearPageEncMaskForGhcbPageExit:
+    OneTimeCallRet SevClearPageEncMaskForGhcbPage
+
+; Check if SEV is enabled, and get the C-bit mask above 31.
+; Modified: EDX
+;
+; The value is returned in the EDX
+GetSevCBitMaskAbove31:
+    xor       edx, edx
+
+    ; Check if SEV is enabled
+    cmp       byte[WORK_AREA_GUEST_TYPE], 1
+    jnz       GetSevCBitMaskAbove31Exit
+
+    mov       edx, dword[SEV_ES_WORK_AREA_ENC_MASK + 4]
+
+GetSevCBitMaskAbove31Exit:
+    OneTimeCallRet GetSevCBitMaskAbove31
+
 ; Check if Secure Encrypted Virtualization (SEV) features are enabled.
 ;
 ; Register usage is tight in this routine, so multiple calls for the
@@ -249,32 +334,6 @@ SevExit:
 
     OneTimeCallRet CheckSevFeatures
 
-; Check if Secure Encrypted Virtualization - Encrypted State (SEV-ES) feature
-; is enabled.
-;
-; Modified:  EAX
-;
-; If SEV-ES is enabled then EAX will be non-zero.
-; If SEV-ES is disabled then EAX will be zero.
-;
-IsSevEsEnabled:
-    xor       eax, eax
-
-    ; During CheckSevFeatures, the WORK_AREA_GUEST_TYPE is set
-    ; to 1 if SEV is enabled.
-    cmp       byte[WORK_AREA_GUEST_TYPE], 1
-    jne       SevEsDisabled
-
-    ; During CheckSevFeatures, the SEV_ES_WORK_AREA was set to 1 if
-    ; SEV-ES is enabled.
-    cmp       byte[SEV_ES_WORK_AREA], 1
-    jne       SevEsDisabled
-
-    mov       eax, 1
-
-SevEsDisabled:
-    OneTimeCallRet IsSevEsEnabled
-
 ; Start of #VC exception handling routines
 ;
 
diff --git a/OvmfPkg/ResetVector/Ia32/PageTables64.asm b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
index f688909f1c7d..07b6ca070909 100644
--- a/OvmfPkg/ResetVector/Ia32/PageTables64.asm
+++ b/OvmfPkg/ResetVector/Ia32/PageTables64.asm
@@ -46,16 +46,13 @@ SetCr3ForPageTables64:
     ; work area when detected.
     mov     byte[WORK_AREA_GUEST_TYPE], 0
 
+    ; Check whether the SEV is active and populate the SevEsWorkArea
     OneTimeCall   CheckSevFeatures
-    xor     edx, edx
-    test    eax, eax
-    jz      SevNotActive
 
-    ; If SEV is enabled, C-bit is always above 31
-    sub     eax, 32
-    bts     edx, eax
-
-SevNotActive:
+    ; If SEV is enabled, the C-bit position is always above 31.
+    ; The mask will be saved in the EDX and applied during the
+    ; the page table build below.
+    OneTimeCall   GetSevCBitMaskAbove31
 
     ;
     ; For OVMF, build some initial page tables at
@@ -105,44 +102,8 @@ pageTableEntriesLoop:
     mov     [(ecx * 8 + PT_ADDR (0x2000 - 8)) + 4], edx
     loop    pageTableEntriesLoop
 
-    OneTimeCall   IsSevEsEnabled
-    test    eax, eax
-    jz      SetCr3
-
-    ;
-    ; The initial GHCB will live at GHCB_BASE and needs to be un-encrypted.
-    ; This requires the 2MB page for this range be broken down into 512 4KB
-    ; pages.  All will be marked encrypted, except for the GHCB.
-    ;
-    mov     ecx, (GHCB_BASE >> 21)
-    mov     eax, GHCB_PT_ADDR + PAGE_PDP_ATTR
-    mov     [ecx * 8 + PT_ADDR (0x2000)], eax
-
-    ;
-    ; Page Table Entries (512 * 4KB entries => 2MB)
-    ;
-    mov     ecx, 512
-pageTableEntries4kLoop:
-    mov     eax, ecx
-    dec     eax
-    shl     eax, 12
-    add     eax, GHCB_BASE & 0xFFE0_0000
-    add     eax, PAGE_4K_PDE_ATTR
-    mov     [ecx * 8 + GHCB_PT_ADDR - 8], eax
-    mov     [(ecx * 8 + GHCB_PT_ADDR - 8) + 4], edx
-    loop    pageTableEntries4kLoop
-
-    ;
-    ; Clear the encryption bit from the GHCB entry
-    ;
-    mov     ecx, (GHCB_BASE & 0x1F_FFFF) >> 12
-    mov     [ecx * 8 + GHCB_PT_ADDR + 4], strict dword 0
-
-    mov     ecx, GHCB_SIZE / 4
-    xor     eax, eax
-clearGhcbMemoryLoop:
-    mov     dword[ecx * 4 + GHCB_BASE - 4], eax
-    loop    clearGhcbMemoryLoop
+    ; Clear the C-bit from the GHCB page if the SEV-ES is enabled.
+    OneTimeCall   SevClearPageEncMaskForGhcbPage
 
 SetCr3:
     ;
-- 
2.17.1