[PATCH v2 08/31] OvmfPkg/XenResetVector: Allow to jumpstart from either hvmloader or PVH

[Anthony PERARD <anthony.perard@citrix.com>]

This patch allows the ResetVector to be run indenpendently from build
time addresses.

The goal of the patch is to avoid having to create RAM just below 4G
when creating a Xen PVH guest while been compatible with the way
hvmloader currently load OVMF, just below 4G.

Only the new PVH entry point will do the calculation.

The ResetVector will figure out its current running address by creating
a temporary stack, make a call and calculate the difference between the
build time address and the address at run time.

This patch copies and make the necessary modification to some other asm
files:
- copy of UefiCpuPkg/.../Flat32ToFlat64.asm:
  Allow Transition32FlatTo64Flat to been runnned from anywhere in memory
_ copy of UefiCpuPkg/../SearchForBfvBase.asm:
  Add a extra parameter to indicate where to start the search for the
  boot firmware volume.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 OvmfPkg/XenResetVector/Ia16/Real16ToFlat32.asm                                    |  3 ++
 {UefiCpuPkg/ResetVector/Vtf0 => OvmfPkg/XenResetVector}/Ia32/Flat32ToFlat64.asm   | 25 ++++++++++++++--
 {UefiCpuPkg/ResetVector/Vtf0 => OvmfPkg/XenResetVector}/Ia32/SearchForBfvBase.asm | 19 +++++++++----
 OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm                                        | 30 ++++++++++++++++++--
 4 files changed, 66 insertions(+), 11 deletions(-)

diff --git a/OvmfPkg/XenResetVector/Ia16/Real16ToFlat32.asm b/OvmfPkg/XenResetVector/Ia16/Real16ToFlat32.asm
index e22e92c8a6..eebced6ced 100644
--- a/OvmfPkg/XenResetVector/Ia16/Real16ToFlat32.asm
+++ b/OvmfPkg/XenResetVector/Ia16/Real16ToFlat32.asm
@@ -61,6 +61,9 @@ jumpTo32BitAndLandHere:
     mov     gs, ax
     mov     ss, ax
 
+    ; parameter for Flat32SearchForBfvBase
+    xor     eax, eax ; Start searching from top of 4GB for BfvBase
+
     OneTimeCallRet TransitionFromReal16To32BitFlat
 
 ALIGN   2
diff --git a/UefiCpuPkg/ResetVector/Vtf0/Ia32/Flat32ToFlat64.asm b/OvmfPkg/XenResetVector/Ia32/Flat32ToFlat64.asm
similarity index 69%
copy from UefiCpuPkg/ResetVector/Vtf0/Ia32/Flat32ToFlat64.asm
copy to OvmfPkg/XenResetVector/Ia32/Flat32ToFlat64.asm
index 5b6b375330..ca03ea43e0 100644
--- a/UefiCpuPkg/ResetVector/Vtf0/Ia32/Flat32ToFlat64.asm
+++ b/OvmfPkg/XenResetVector/Ia32/Flat32ToFlat64.asm
@@ -3,6 +3,8 @@
 ; Transition from 32 bit flat protected mode into 64 bit flat protected mode
 ;
 ; Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2019, Citrix Systems, Inc.
+;
 ; This program and the accompanying materials
 ; are licensed and made available under the terms and conditions of the BSD License
 ; which accompanies this distribution.  The full text of the license may be found at
@@ -16,7 +18,7 @@
 BITS    32
 
 ;
-; Modified:  EAX
+; Modified:  EAX, EBX, ECX, EDX, ESP
 ;
 Transition32FlatTo64Flat:
 
@@ -35,10 +37,29 @@ Transition32FlatTo64Flat:
     bts     eax, 31                     ; set PG
     mov     cr0, eax                    ; enable paging
 
-    jmp     LINEAR_CODE64_SEL:ADDR_OF(jumpTo64BitAndLandHere)
+    ; backup ESP
+    mov     ebx, esp
+
+    ;; recalculate delta
+    mov     esp, PVH_SPACE(16)
+    call    .delta
+.delta:
+    pop     edx
+    sub     edx, ADDR_OF(.delta)
+
+    ; push return addr and seg to the stack, then return far
+    push    dword LINEAR_CODE64_SEL
+    mov     eax, ADDR_OF(jumpTo64BitAndLandHere)
+    add     eax, edx ; add delta
+    push    eax
+    retf
+
 BITS    64
 jumpTo64BitAndLandHere:
 
+    ; restore ESP
+    mov     esp, ebx
+
     debugShowPostCode POSTCODE_64BIT_MODE
 
     OneTimeCallRet Transition32FlatTo64Flat
diff --git a/UefiCpuPkg/ResetVector/Vtf0/Ia32/SearchForBfvBase.asm b/OvmfPkg/XenResetVector/Ia32/SearchForBfvBase.asm
similarity index 83%
copy from UefiCpuPkg/ResetVector/Vtf0/Ia32/SearchForBfvBase.asm
copy to OvmfPkg/XenResetVector/Ia32/SearchForBfvBase.asm
index d0c2d8c39c..0519e05601 100644
--- a/UefiCpuPkg/ResetVector/Vtf0/Ia32/SearchForBfvBase.asm
+++ b/OvmfPkg/XenResetVector/Ia32/SearchForBfvBase.asm
@@ -3,6 +3,8 @@
 ; Search for the Boot Firmware Volume (BFV) base address
 ;
 ; Copyright (c) 2008 - 2009, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2019, Citrix Systems, Inc.
+;
 ; This program and the accompanying materials
 ; are licensed and made available under the terms and conditions of the BSD License
 ; which accompanies this distribution.  The full text of the license may be found at
@@ -23,22 +25,26 @@
 BITS    32
 
 ;
-; Modified:  EAX, EBX
+; Modified:  EAX, EBX, ECX
 ; Preserved: EDI, ESP
 ;
+; @param[in]   EAX  Start search from here
 ; @param[out]  EBP  Address of Boot Firmware Volume (BFV)
 ;
 Flat32SearchForBfvBase:
 
-    xor     eax, eax
+    mov     ecx, eax
 searchingForBfvHeaderLoop:
     ;
-    ; We check for a firmware volume at every 4KB address in the top 16MB
-    ; just below 4GB.  (Addresses at 0xffHHH000 where H is any hex digit.)
+    ; We check for a firmware volume at every 4KB address in the 16MB
+    ; just below where we started, ECX.
     ;
     sub     eax, 0x1000
-    cmp     eax, 0xff000000
-    jb      searchedForBfvHeaderButNotFound
+    mov     ebx, ecx
+    sub     ebx, eax
+    cmp     ebx, 0x01000000
+    ; if ECX-EAX > 16MB; jump notfound
+    ja      searchedForBfvHeaderButNotFound
 
     ;
     ; Check FFS GUID
@@ -59,6 +65,7 @@ searchingForBfvHeaderLoop:
     jne     searchingForBfvHeaderLoop
     mov     ebx, eax
     add     ebx, dword [eax + 0x20]
+    cmp     ebx, ecx
     jnz     searchingForBfvHeaderLoop
 
     jmp     searchedForBfvHeaderAndItWasFound
diff --git a/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm b/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm
index 4e55b0ac1f..612b2e9c44 100644
--- a/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm
+++ b/OvmfPkg/XenResetVector/Ia32/XenPVHMain.asm
@@ -19,22 +19,39 @@ BITS    32
 xenPVHMain:
     mov     di, 'BP'
 
-    ; ESP -  Initial value of the EAX register (BIST: Built-in Self Test)
-    mov     esp, eax
+    ; EBP -  Initial value of the EAX register (BIST: Built-in Self Test)
+    mov     ebp, eax
 
     ;; Store "Start of day" struct pointer for later use
     mov     dword[PVH_SPACE (0)], ebx
     mov     dword[PVH_SPACE (4)], 'XPVH'
 
+    ;; calculate delta between build-addr and run position
+    mov     esp, PVH_SPACE(16)          ; create a temporary stack
+    call    .delta
+.delta:
+    pop     edx                         ; get addr of .delta
+    sub     edx, ADDR_OF(.delta)        ; calculate delta
+
     cli
 
+    ;; Find address of GDT and gdtr and fix the later
     mov     ebx, ADDR_OF(gdtr)
+    add     ebx, edx                    ; add delta gdtr
+    mov     eax, ADDR_OF(GDT_BASE)
+    add     eax, edx                    ; add delta to GDT_BASE
+    mov     dword[ebx + 2], eax         ; fix GDT_BASE addr in gdtr
     lgdt    [ebx]
 
     mov     eax, SEC_DEFAULT_CR0
     mov     cr0, eax
 
-    jmp     LINEAR_CODE_SEL:ADDR_OF(.jmpToNewCodeSeg)
+    ;; push return addr to the stack, then return far
+    push    dword LINEAR_CODE_SEL       ; segment to select
+    mov     eax, ADDR_OF(.jmpToNewCodeSeg) ; return addr
+    add     eax, edx                    ; add delta to return addr
+    push    eax
+    retf
 .jmpToNewCodeSeg:
 
     mov     eax, SEC_DEFAULT_CR4
@@ -47,5 +64,12 @@ xenPVHMain:
     mov     gs, ax
     mov     ss, ax
 
+    ; ESP -  Initial value of the EAX register (BIST: Built-in Self Test)
+    mov     esp, ebp
+
+    ; parameter for Flat32SearchForBfvBase
+    mov     eax, ADDR_OF(fourGigabytes)
+    add     eax, edx ; add delta
+
     ; return to the Main16
     OneTimeCallRet TransitionFromReal16To32BitFlat
-- 
Anthony PERARD


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