/* SPDX-License-Identifier: GPL-2.0
 *
 * Assembly level code for mshv_vtl VTL transition
 *
 * Copyright (c) 2025, Microsoft Corporation.
 *
 * Author:
 *   Naman Jain <namjain@microsoft.com>
 */

#include <linux/linkage.h>
#include <linux/static_call_types.h>
#include <asm/asm.h>
#include <asm/asm-offsets.h>
#include <asm/frame.h>
#include "mshv-asm-offsets.h"

        .text
        .section .noinstr.text, "ax"
/*
 * void __mshv_vtl_return_call(struct mshv_vtl_cpu_context *vtl0)
 *
 * This function is used to context switch between different Virtual Trust Levels.
 * It is marked as 'noinstr' to prevent against instrumentation and debugging facilities.
 * NMIs aren't a problem because the NMI handler saves/restores CR2 specifically to guard
 * against #PFs in NMI context clobbering the guest state.
 */
SYM_FUNC_START(__mshv_vtl_return_call)
        /* Push callee save registers */
        pushq %rbp
        mov %rsp, %rbp
        pushq %r12
        pushq %r13
        pushq %r14
        pushq %r15
        pushq %rbx

        /* register switch to VTL0 clobbers all registers except rax/rcx */
        mov %_ASM_ARG1, %rax

        /* grab rbx/rbp/rsi/rdi/r8-r15 */
        mov MSHV_VTL_CPU_CONTEXT_rbx(%rax), %rbx
        mov MSHV_VTL_CPU_CONTEXT_rbp(%rax), %rbp
        mov MSHV_VTL_CPU_CONTEXT_rsi(%rax), %rsi
        mov MSHV_VTL_CPU_CONTEXT_rdi(%rax), %rdi
        mov MSHV_VTL_CPU_CONTEXT_r8(%rax), %r8
        mov MSHV_VTL_CPU_CONTEXT_r9(%rax), %r9
        mov MSHV_VTL_CPU_CONTEXT_r10(%rax), %r10
        mov MSHV_VTL_CPU_CONTEXT_r11(%rax), %r11
        mov MSHV_VTL_CPU_CONTEXT_r12(%rax), %r12
        mov MSHV_VTL_CPU_CONTEXT_r13(%rax), %r13
        mov MSHV_VTL_CPU_CONTEXT_r14(%rax), %r14
        mov MSHV_VTL_CPU_CONTEXT_r15(%rax), %r15

        mov MSHV_VTL_CPU_CONTEXT_cr2(%rax), %rdx
        mov %rdx, %cr2
        mov MSHV_VTL_CPU_CONTEXT_rdx(%rax), %rdx

        /* stash host registers on stack */
        pushq %rax
        pushq %rcx

        xor %ecx, %ecx

        /* make a hypercall to switch VTL */
        call STATIC_CALL_TRAMP_STR(__mshv_vtl_return_hypercall)

        /* stash guest registers on stack, restore saved host copies */
        pushq %rax
        pushq %rcx
        mov 16(%rsp), %rcx
        mov 24(%rsp), %rax

        mov %rdx, MSHV_VTL_CPU_CONTEXT_rdx(%rax)
        mov %cr2, %rdx
        mov %rdx, MSHV_VTL_CPU_CONTEXT_cr2(%rax)
        pop MSHV_VTL_CPU_CONTEXT_rcx(%rax)
        pop MSHV_VTL_CPU_CONTEXT_rax(%rax)
        add $16, %rsp

        /* save rbx/rbp/rsi/rdi/r8-r15 */
        mov %rbx, MSHV_VTL_CPU_CONTEXT_rbx(%rax)
        mov %rbp, MSHV_VTL_CPU_CONTEXT_rbp(%rax)
        mov %rsi, MSHV_VTL_CPU_CONTEXT_rsi(%rax)
        mov %rdi, MSHV_VTL_CPU_CONTEXT_rdi(%rax)
        mov %r8,  MSHV_VTL_CPU_CONTEXT_r8(%rax)
        mov %r9,  MSHV_VTL_CPU_CONTEXT_r9(%rax)
        mov %r10, MSHV_VTL_CPU_CONTEXT_r10(%rax)
        mov %r11, MSHV_VTL_CPU_CONTEXT_r11(%rax)
        mov %r12, MSHV_VTL_CPU_CONTEXT_r12(%rax)
        mov %r13, MSHV_VTL_CPU_CONTEXT_r13(%rax)
        mov %r14, MSHV_VTL_CPU_CONTEXT_r14(%rax)
        mov %r15, MSHV_VTL_CPU_CONTEXT_r15(%rax)

        /* pop callee-save registers r12-r15, rbx */
        pop %rbx
        pop %r15
        pop %r14
        pop %r13
        pop %r12

        pop %rbp
        RET
SYM_FUNC_END(__mshv_vtl_return_call)
/*
 * Make sure that static_call_key symbol: __SCK____mshv_vtl_return_hypercall is accessible here.
 * Below code is inspired from __ADDRESSABLE(sym) macro. Symbol name is kept simple, to avoid
 * naming it something like "__UNIQUE_ID_addressable___SCK____mshv_vtl_return_hypercall_662.0"
 * which would otherwise have been generated by the macro.
 */
        .section        .discard.addressable,"aw"
        .align 8
        .type   mshv_vtl_return_sym, @object
        .size   mshv_vtl_return_sym, 8
mshv_vtl_return_sym:
        .quad   __SCK____mshv_vtl_return_hypercall