audk/OvmfPkg/XenResetVector/Ia32/PageTables64.asm

;------------------------------------------------------------------------------
; @file
; Sets the CR3 register for 64-bit paging
;
; Copyright (c) 2008 - 2013, Intel Corporation. All rights reserved.<BR>
; Copyright (c) 2019, Citrix Systems, Inc.
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
;------------------------------------------------------------------------------

BITS    32

%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_2M_PDE_ATTR (PAGE_2M_MBO + \
                          PAGE_ACCESSED + \
                          PAGE_DIRTY + \
                          PAGE_READ_WRITE + \
                          PAGE_PRESENT)

%define PAGE_PDP_ATTR (PAGE_ACCESSED + \
                       PAGE_READ_WRITE + \
                       PAGE_PRESENT)

; Check if Secure Encrypted Virtualization (SEV) feature is enabled
;
; If SEV is enabled then EAX will be at least 32
; If SEV is disabled then EAX will be zero.
;
CheckSevFeature:
    ; Check if we have a valid (0x8000_001F) CPUID leaf
    mov       eax, 0x80000000
    cpuid

    ; This check should fail on Intel or Non SEV AMD CPUs. In future if
    ; Intel CPUs supports this CPUID leaf then we are guranteed to have exact
    ; same bit definition.
    cmp       eax, 0x8000001f
    jl        NoSev

    ; Check for memory encryption feature:
    ;  CPUID  Fn8000_001F[EAX] - Bit 1
    ;
    mov       eax,  0x8000001f
    cpuid
    bt        eax, 1
    jnc       NoSev

    ; Check if memory encryption is enabled
    ;  MSR_0xC0010131 - Bit 0 (SEV enabled)
    mov       ecx, 0xc0010131
    rdmsr
    bt        eax, 0
    jnc       NoSev

    ; Get pte bit position to enable memory encryption
    ; CPUID Fn8000_001F[EBX] - Bits 5:0
    ;
    mov       eax, ebx
    and       eax, 0x3f
    jmp       SevExit

NoSev:
    xor       eax, eax

SevExit:
    OneTimeCallRet CheckSevFeature

;
; Modified:  EAX, EBX, ECX, EDX
;
SetCr3ForPageTables64:

    OneTimeCall   CheckSevFeature
    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:

    ;
    ; For OVMF, build some initial page tables at
    ; PcdOvmfSecPageTablesBase - (PcdOvmfSecPageTablesBase + 0x6000).
    ;
    ; This range should match with PcdOvmfSecPageTablesSize which is
    ; declared in the FDF files.
    ;
    ; At the end of PEI, the pages tables will be rebuilt into a
    ; more permanent location by DxeIpl.
    ;

    mov     ecx, 6 * 0x1000 / 4
    xor     eax, eax
clearPageTablesMemoryLoop:
    mov     dword[ecx * 4 + PT_ADDR (0) - 4], eax
    loop    clearPageTablesMemoryLoop

    ;
    ; Top level Page Directory Pointers (1 * 512GB entry)
    ;
    mov     dword[PT_ADDR (0)], PT_ADDR (0x1000) + PAGE_PDP_ATTR
    mov     dword[PT_ADDR (4)], edx

    ;
    ; Next level Page Directory Pointers (4 * 1GB entries => 4GB)
    ;
    mov     dword[PT_ADDR (0x1000)], PT_ADDR (0x2000) + PAGE_PDP_ATTR
    mov     dword[PT_ADDR (0x1004)], edx
    mov     dword[PT_ADDR (0x1008)], PT_ADDR (0x3000) + PAGE_PDP_ATTR
    mov     dword[PT_ADDR (0x100C)], edx
    mov     dword[PT_ADDR (0x1010)], PT_ADDR (0x4000) + PAGE_PDP_ATTR
    mov     dword[PT_ADDR (0x1014)], edx
    mov     dword[PT_ADDR (0x1018)], PT_ADDR (0x5000) + PAGE_PDP_ATTR
    mov     dword[PT_ADDR (0x101C)], edx

    ;
    ; Page Table Entries (2048 * 2MB entries => 4GB)
    ;
    mov     ecx, 0x800
pageTableEntriesLoop:
    mov     eax, ecx
    dec     eax
    shl     eax, 21
    add     eax, PAGE_2M_PDE_ATTR
    mov     [ecx * 8 + PT_ADDR (0x2000 - 8)], eax
    mov     [(ecx * 8 + PT_ADDR (0x2000 - 8)) + 4], edx
    loop    pageTableEntriesLoop

    ;
    ; Set CR3 now that the paging structures are available
    ;
    mov     eax, PT_ADDR (0)
    mov     cr3, eax

    OneTimeCallRet SetCr3ForPageTables64