/* SPDX-License-Identifier: GPL-2.0 */
/*
 * The actual FRED entry points.
 */

#include <linux/export.h>
#include <linux/kvm_types.h>

#include <asm/asm.h>
#include <asm/fred.h>
#include <asm/segment.h>

#include "calling.h"

        .code64
        .section .noinstr.text, "ax"

.macro FRED_ENTER
        UNWIND_HINT_END_OF_STACK
        ANNOTATE_NOENDBR
        PUSH_AND_CLEAR_REGS
        movq    %rsp, %rdi      /* %rdi -> pt_regs */
.endm

.macro FRED_EXIT
        UNWIND_HINT_REGS
        POP_REGS
.endm

/*
 * The new RIP value that FRED event delivery establishes is
 * IA32_FRED_CONFIG & ~FFFH for events that occur in ring 3.
 * Thus the FRED ring 3 entry point must be 4K page aligned.
 */
        .align 4096

SYM_CODE_START_NOALIGN(asm_fred_entrypoint_user)
        FRED_ENTER
        call    fred_entry_from_user
SYM_INNER_LABEL(asm_fred_exit_user, SYM_L_GLOBAL)
        FRED_EXIT
1:      ERETU

        _ASM_EXTABLE_TYPE(1b, asm_fred_entrypoint_user, EX_TYPE_ERETU)
SYM_CODE_END(asm_fred_entrypoint_user)

/*
 * The new RIP value that FRED event delivery establishes is
 * (IA32_FRED_CONFIG & ~FFFH) + 256 for events that occur in
 * ring 0, i.e., asm_fred_entrypoint_user + 256.
 */
        .org asm_fred_entrypoint_user + 256, 0xcc
SYM_CODE_START_NOALIGN(asm_fred_entrypoint_kernel)
        FRED_ENTER
        call    fred_entry_from_kernel
        FRED_EXIT
        ERETS
SYM_CODE_END(asm_fred_entrypoint_kernel)

#if IS_ENABLED(CONFIG_KVM_INTEL)
SYM_FUNC_START(asm_fred_entry_from_kvm)
        ANNOTATE_NOENDBR
        push %rbp
        mov %rsp, %rbp

        UNWIND_HINT_SAVE

        /*
         * Both IRQ and NMI from VMX can be handled on current task stack
         * because there is no need to protect from reentrancy and the call
         * stack leading to this helper is effectively constant and shallow
         * (relatively speaking). Do the same when FRED is active, i.e., no
         * need to check current stack level for a stack switch.
         *
         * Emulate the FRED-defined redzone and stack alignment.
         */
        sub $(FRED_CONFIG_REDZONE_AMOUNT << 6), %rsp
        and $FRED_STACK_FRAME_RSP_MASK, %rsp

        /*
         * Start to push a FRED stack frame, which is always 64 bytes:
         *
         * +--------+-----------------+
         * | Bytes  | Usage           |
         * +--------+-----------------+
         * | 63:56  | Reserved        |
         * | 55:48  | Event Data      |
         * | 47:40  | SS + Event Info |
         * | 39:32  | RSP             |
         * | 31:24  | RFLAGS          |
         * | 23:16  | CS + Aux Info   |
         * |  15:8  | RIP             |
         * |   7:0  | Error Code      |
         * +--------+-----------------+
         */
        push $0                         /* Reserved, must be 0 */
        push $0                         /* Event data, 0 for IRQ/NMI */
        push %rdi                       /* fred_ss handed in by the caller */
        push %rbp
        pushf
        push $__KERNEL_CS

        /*
         * Unlike the IDT event delivery, FRED _always_ pushes an error code
         * after pushing the return RIP, thus the CALL instruction CANNOT be
         * used here to push the return RIP, otherwise there is no chance to
         * push an error code before invoking the IRQ/NMI handler.
         *
         * Use LEA to get the return RIP and push it, then push an error code.
         */
        lea 1f(%rip), %rax
        push %rax                               /* Return RIP */
        push $0                                 /* Error code, 0 for IRQ/NMI */

        PUSH_AND_CLEAR_REGS clear_callee=0 unwind_hint=0

        movq %rsp, %rdi                         /* %rdi -> pt_regs */
        /*
         * At this point: {rdi, rsi, rdx, rcx, r8, r9}, {r10, r11}, {rax, rdx}
         * are clobbered, which corresponds to: arguments, extra caller-saved
         * and return. All registers a C function is allowed to clobber.
         *
         * Notably, the callee-saved registers: {rbx, r12, r13, r14, r15}
         * are untouched, with the exception of rbp, which carries the stack
         * frame and will be restored before exit.
         *
         * Further calling another C function will not alter this state.
         */
        call __fred_entry_from_kvm              /* Call the C entry point */

        /*
         * When FRED, use ERETS to potentially clear NMIs, otherwise simply
         * restore the stack pointer.
         */
        ALTERNATIVE "nop; nop; mov %rbp, %rsp", \
                    __stringify(add $C_PTREGS_SIZE, %rsp; ERETS), \
                    X86_FEATURE_FRED

1:      /*
         * Objtool doesn't understand ERETS, and the cfi register state is
         * different from initial_func_cfi due to PUSH_REGS. Tell it the state
         * is similar to where UNWIND_HINT_SAVE is.
         */
        UNWIND_HINT_RESTORE

        pop %rbp
        RET

SYM_FUNC_END(asm_fred_entry_from_kvm)
EXPORT_SYMBOL_FOR_KVM(asm_fred_entry_from_kvm);
#endif