/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (C) 2014 Intel Corporation; author Matt Fleming
 *
 * Support for invoking 32-bit EFI runtime services from a 64-bit
 * kernel.
 *
 * The below thunking functions are only used after ExitBootServices()
 * has been called. This simplifies things considerably as compared with
 * the early EFI thunking because we can leave all the kernel state
 * intact (GDT, IDT, etc) and simply invoke the 32-bit EFI runtime
 * services from __KERNEL32_CS. This means we can continue to service
 * interrupts across an EFI mixed mode call.
 *
 * We do however, need to handle the fact that we're running in a full
 * 64-bit virtual address space. Things like the stack and instruction
 * addresses need to be accessible by the 32-bit firmware, so we rely on
 * using the identity mappings in the EFI page table to access the stack
 * and kernel text (see efi_setup_page_tables()).
 */

#include <linux/linkage.h>
#include <linux/objtool.h>
#include <asm/page_types.h>
#include <asm/segment.h>

        .text
        .code64
SYM_FUNC_START(__efi64_thunk)
STACK_FRAME_NON_STANDARD __efi64_thunk
        push    %rbp
        push    %rbx

        /*
         * Switch to 1:1 mapped 32-bit stack pointer.
         */
        movq    %rsp, %rax
        movq    efi_mixed_mode_stack_pa(%rip), %rsp
        push    %rax

        /*
         * Copy args passed via the stack
         */
        subq    $0x24, %rsp
        movq    0x18(%rax), %rbp
        movq    0x20(%rax), %rbx
        movq    0x28(%rax), %rax
        movl    %ebp, 0x18(%rsp)
        movl    %ebx, 0x1c(%rsp)
        movl    %eax, 0x20(%rsp)

        /*
         * Calculate the physical address of the kernel text.
         */
        movq    $__START_KERNEL_map, %rax
        subq    phys_base(%rip), %rax

        leaq    1f(%rip), %rbp
        leaq    2f(%rip), %rbx
        subq    %rax, %rbp
        subq    %rax, %rbx

        movl    %ebx, 0x0(%rsp)         /* return address */
        movl    %esi, 0x4(%rsp)
        movl    %edx, 0x8(%rsp)
        movl    %ecx, 0xc(%rsp)
        movl    %r8d, 0x10(%rsp)
        movl    %r9d, 0x14(%rsp)

        /* Switch to 32-bit descriptor */
        pushq   $__KERNEL32_CS
        pushq   %rdi                    /* EFI runtime service address */
        lretq

        // This return instruction is not needed for correctness, as it will
        // never be reached. It only exists to make objtool happy, which will
        // otherwise complain about unreachable instructions in the callers.
        RET
SYM_FUNC_END(__efi64_thunk)

        .section ".rodata", "a", @progbits
        .balign 16
SYM_DATA_START(__efi64_thunk_ret_tramp)
1:      movq    0x20(%rsp), %rsp
        pop     %rbx
        pop     %rbp
        ret
        int3

        .code32
2:      pushl   $__KERNEL_CS
        pushl   %ebp
        lret
SYM_DATA_END(__efi64_thunk_ret_tramp)

        .bss
        .balign 8
SYM_DATA(efi_mixed_mode_stack_pa, .quad 0)