arch/riscv/kernel/head.S

root/arch/riscv/kernel/head.S
/* SPDX-License-Identifier: GPL-2.0-only */
/*
 * Copyright (C) 2012 Regents of the University of California
 */

#include <asm/asm-offsets.h>
#include <asm/asm.h>
#include <linux/init.h>
#include <linux/linkage.h>
#include <asm/thread_info.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/csr.h>
#include <asm/hwcap.h>
#include <asm/image.h>
#include <asm/scs.h>
#include <asm/xip_fixup.h>
#include <asm/usercfi.h>
#include "efi-header.S"

__HEAD
SYM_CODE_START(_start)
        /*
         * Image header expected by Linux boot-loaders. The image header data
         * structure is described in asm/image.h.
         * Do not modify it without modifying the structure and all bootloaders
         * that expects this header format!!
         */
#ifdef CONFIG_EFI
        /*
         * This instruction decodes to "MZ" ASCII required by UEFI.
         */
        c.li s4,-13
        j _start_kernel
#else
        /* jump to start kernel */
        j _start_kernel
        /* reserved */
        .word 0
#endif
        .balign 8
#ifdef CONFIG_RISCV_M_MODE
        /* Image load offset (0MB) from start of RAM for M-mode */
        .dword 0
#else
#if __riscv_xlen == 64
        /* Image load offset(2MB) from start of RAM */
        .dword 0x200000
#else
        /* Image load offset(4MB) from start of RAM */
        .dword 0x400000
#endif
#endif
        /* Effective size of kernel image */
        .dword _end - _start
        .dword __HEAD_FLAGS
        .word RISCV_HEADER_VERSION
        .word 0
        .dword 0
        .ascii RISCV_IMAGE_MAGIC
        .balign 4
        .ascii RISCV_IMAGE_MAGIC2
#ifdef CONFIG_EFI
        .word pe_head_start - _start
pe_head_start:

        __EFI_PE_HEADER
#else
        .word 0
#endif

.align 2
#ifdef CONFIG_MMU
        .global relocate_enable_mmu
relocate_enable_mmu:
        /* Relocate return address */
        la a1, kernel_map
        XIP_FIXUP_OFFSET a1
        REG_L a1, KERNEL_MAP_VIRT_ADDR(a1)
        la a2, _start
        sub a1, a1, a2
        add ra, ra, a1

        /* Point stvec to virtual address of intruction after satp write */
        la a2, 1f
        add a2, a2, a1
        csrw CSR_TVEC, a2

        /* Compute satp for kernel page tables, but don't load it yet */
        srl a2, a0, PAGE_SHIFT
        la a1, satp_mode
        XIP_FIXUP_OFFSET a1
        REG_L a1, 0(a1)
        or a2, a2, a1

        /*
         * Load trampoline page directory, which will cause us to trap to
         * stvec if VA != PA, or simply fall through if VA == PA.  We need a
         * full fence here because setup_vm() just wrote these PTEs and we need
         * to ensure the new translations are in use.
         */
        la a0, trampoline_pg_dir
        XIP_FIXUP_OFFSET a0
        srl a0, a0, PAGE_SHIFT
        or a0, a0, a1
        sfence.vma
        csrw CSR_SATP, a0
.align 2
1:
        /* Set trap vector to spin forever to help debug */
        la a0, .Lsecondary_park
        csrw CSR_TVEC, a0

        /* Reload the global pointer */
        load_global_pointer

        /*
         * Switch to kernel page tables.  A full fence is necessary in order to
         * avoid using the trampoline translations, which are only correct for
         * the first superpage.  Fetching the fence is guaranteed to work
         * because that first superpage is translated the same way.
         */
        csrw CSR_SATP, a2
        sfence.vma

        ret
#endif /* CONFIG_MMU */
#ifdef CONFIG_SMP
        .global secondary_start_sbi
secondary_start_sbi:
        /* Mask all interrupts */
        csrw CSR_IE, zero
        csrw CSR_IP, zero

#ifndef CONFIG_RISCV_M_MODE
        /* Enable time CSR */
        li t0, 0x2
        csrw CSR_SCOUNTEREN, t0
#endif

        /* Load the global pointer */
        load_global_pointer

        /*
         * Disable FPU & VECTOR to detect illegal usage of
         * floating point or vector in kernel space
         */
        li t0, SR_FS_VS
        csrc CSR_STATUS, t0

        /* Set trap vector to spin forever to help debug */
        la a3, .Lsecondary_park
        csrw CSR_TVEC, a3

        /* a0 contains the hartid & a1 contains boot data */
        li a2, SBI_HART_BOOT_TASK_PTR_OFFSET
        XIP_FIXUP_OFFSET a2
        add a2, a2, a1
        REG_L tp, (a2)
        li a3, SBI_HART_BOOT_STACK_PTR_OFFSET
        XIP_FIXUP_OFFSET a3
        add a3, a3, a1
        REG_L sp, (a3)

.Lsecondary_start_common:

#ifdef CONFIG_MMU
        /* Enable virtual memory and relocate to virtual address */
        la a0, swapper_pg_dir
        XIP_FIXUP_OFFSET a0
        call relocate_enable_mmu
#endif
        call .Lsetup_trap_vector
#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)
        li a7, SBI_EXT_FWFT
        li a6, SBI_EXT_FWFT_SET
        li a0, SBI_FWFT_SHADOW_STACK
        li a1, 1 /* enable supervisor to access shadow stack access */
        li a2, SBI_FWFT_SET_FLAG_LOCK
        ecall
        beqz a0, 1f
        la a1, riscv_nousercfi
        li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI
        REG_S a0, (a1)
1:
#endif
        scs_load_current
        call smp_callin
#endif /* CONFIG_SMP */

.align 2
.Lsecondary_park:
        /*
         * Park this hart if we:
         *  - have too many harts on CONFIG_RISCV_BOOT_SPINWAIT
         *  - receive an early trap, before setup_trap_vector finished
         *  - fail in smp_callin(), as a successful one wouldn't return
         */
        wfi
        j .Lsecondary_park

.align 2
.Lsetup_trap_vector:
        /* Set trap vector to exception handler */
        la a0, handle_exception
        csrw CSR_TVEC, a0

        /*
         * Set sup0 scratch register to 0, indicating to exception vector that
         * we are presently executing in kernel.
         */
        csrw CSR_SCRATCH, zero
        ret

SYM_CODE_END(_start)

SYM_CODE_START(_start_kernel)
        /* Mask all interrupts */
        csrw CSR_IE, zero
        csrw CSR_IP, zero

#ifdef CONFIG_RISCV_M_MODE
        /* flush the instruction cache */
        fence.i

        /* Reset all registers except ra, a0, a1 */
        call reset_regs

        /*
         * Setup a PMP to permit access to all of memory.  Some machines may
         * not implement PMPs, so we set up a quick trap handler to just skip
         * touching the PMPs on any trap.
         */
        la a0, .Lpmp_done
        csrw CSR_TVEC, a0

        li a0, -1
        csrw CSR_PMPADDR0, a0
        li a0, (PMP_A_NAPOT | PMP_R | PMP_W | PMP_X)
        csrw CSR_PMPCFG0, a0
.align 2
.Lpmp_done:

        /*
         * The hartid in a0 is expected later on, and we have no firmware
         * to hand it to us.
         */
        csrr a0, CSR_MHARTID
#else
        /* Enable time CSR */
        li t0, 0x2
        csrw CSR_SCOUNTEREN, t0
#endif /* CONFIG_RISCV_M_MODE */

        /* Load the global pointer */
        load_global_pointer

        /*
         * Disable FPU & VECTOR to detect illegal usage of
         * floating point or vector in kernel space
         */
        li t0, SR_FS_VS
        csrc CSR_STATUS, t0

#ifdef CONFIG_RISCV_BOOT_SPINWAIT
        li t0, CONFIG_NR_CPUS
        blt a0, t0, .Lgood_cores
        tail .Lsecondary_park
.Lgood_cores:

        /* The lottery system is only required for spinwait booting method */
#ifndef CONFIG_XIP_KERNEL
        /* Pick one hart to run the main boot sequence */
        la a3, hart_lottery
        li a2, 1
        amoadd.w a3, a2, (a3)
        bnez a3, .Lsecondary_start

#else
        /* hart_lottery in flash contains a magic number */
        la a3, hart_lottery
        mv a2, a3
        XIP_FIXUP_OFFSET a2
        XIP_FIXUP_FLASH_OFFSET a3
        lw t1, (a3)
        amoswap.w t0, t1, (a2)
        /* first time here if hart_lottery in RAM is not set */
        beq t0, t1, .Lsecondary_start

#endif /* CONFIG_XIP */
#endif /* CONFIG_RISCV_BOOT_SPINWAIT */

#ifdef CONFIG_XIP_KERNEL
        la sp, _end + THREAD_SIZE
        XIP_FIXUP_OFFSET sp
        mv s0, a0
        mv s1, a1
        call __copy_data

        /* Restore a0 & a1 copy */
        mv a0, s0
        mv a1, s1
#endif

#ifndef CONFIG_XIP_KERNEL
        /* Clear BSS for flat non-ELF images */
        la a3, __bss_start
        la a4, __bss_stop
        ble a4, a3, .Lclear_bss_done
.Lclear_bss:
        REG_S zero, (a3)
        add a3, a3, RISCV_SZPTR
        blt a3, a4, .Lclear_bss
.Lclear_bss_done:
#endif
        la a2, boot_cpu_hartid
        XIP_FIXUP_OFFSET a2
        REG_S a0, (a2)

        /* Initialize page tables and relocate to virtual addresses */
        la tp, init_task
        la sp, init_thread_union + THREAD_SIZE
        XIP_FIXUP_OFFSET sp
        addi sp, sp, -PT_SIZE_ON_STACK
        scs_load_init_stack
#ifdef CONFIG_BUILTIN_DTB
        la a0, __dtb_start
        XIP_FIXUP_OFFSET a0
#else
        mv a0, a1
#endif /* CONFIG_BUILTIN_DTB */
        /* Set trap vector to spin forever to help debug */
        la a3, .Lsecondary_park
        csrw CSR_TVEC, a3
        call setup_vm
#ifdef CONFIG_MMU
        la a0, early_pg_dir
        XIP_FIXUP_OFFSET a0
        call relocate_enable_mmu
#endif /* CONFIG_MMU */

        call .Lsetup_trap_vector
        /* Restore C environment */
        la tp, init_task
        la sp, init_thread_union + THREAD_SIZE
        addi sp, sp, -PT_SIZE_ON_STACK
#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)
        li a7, SBI_EXT_FWFT
        li a6, SBI_EXT_FWFT_SET
        li a0, SBI_FWFT_SHADOW_STACK
        li a1, 1 /* enable supervisor to access shadow stack access */
        li a2, SBI_FWFT_SET_FLAG_LOCK
        ecall
        beqz a0, 1f
        la a1, riscv_nousercfi
        li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI
        REG_S a0, (a1)
1:
#endif
        scs_load_current

#ifdef CONFIG_KASAN
        call kasan_early_init
#endif
        /* Start the kernel */
        call soc_early_init
        tail start_kernel

#ifdef CONFIG_RISCV_BOOT_SPINWAIT
.Lsecondary_start:
        /* Set trap vector to spin forever to help debug */
        la a3, .Lsecondary_park
        csrw CSR_TVEC, a3

        slli a3, a0, LGREG
        la a1, __cpu_spinwait_stack_pointer
        XIP_FIXUP_OFFSET a1
        la a2, __cpu_spinwait_task_pointer
        XIP_FIXUP_OFFSET a2
        add a1, a3, a1
        add a2, a3, a2

        /*
         * This hart didn't win the lottery, so we wait for the winning hart to
         * get far enough along the boot process that it should continue.
         */
.Lwait_for_cpu_up:
        /* FIXME: We should WFI to save some energy here. */
        REG_L sp, (a1)
        REG_L tp, (a2)
        beqz sp, .Lwait_for_cpu_up
        beqz tp, .Lwait_for_cpu_up
        fence

        tail .Lsecondary_start_common
#endif /* CONFIG_RISCV_BOOT_SPINWAIT */

SYM_CODE_END(_start_kernel)

#ifdef CONFIG_RISCV_M_MODE
SYM_CODE_START_LOCAL(reset_regs)
        li      sp, 0
        li      gp, 0
        li      tp, 0
        li      t0, 0
        li      t1, 0
        li      t2, 0
        li      s0, 0
        li      s1, 0
        li      a2, 0
        li      a3, 0
        li      a4, 0
        li      a5, 0
        li      a6, 0
        li      a7, 0
        li      s2, 0
        li      s3, 0
        li      s4, 0
        li      s5, 0
        li      s6, 0
        li      s7, 0
        li      s8, 0
        li      s9, 0
        li      s10, 0
        li      s11, 0
        li      t3, 0
        li      t4, 0
        li      t5, 0
        li      t6, 0
        csrw    CSR_SCRATCH, 0

#ifdef CONFIG_FPU
        csrr    t0, CSR_MISA
        andi    t0, t0, (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D)
        beqz    t0, .Lreset_regs_done_fpu

        li      t1, SR_FS
        csrs    CSR_STATUS, t1
        fmv.s.x f0, zero
        fmv.s.x f1, zero
        fmv.s.x f2, zero
        fmv.s.x f3, zero
        fmv.s.x f4, zero
        fmv.s.x f5, zero
        fmv.s.x f6, zero
        fmv.s.x f7, zero
        fmv.s.x f8, zero
        fmv.s.x f9, zero
        fmv.s.x f10, zero
        fmv.s.x f11, zero
        fmv.s.x f12, zero
        fmv.s.x f13, zero
        fmv.s.x f14, zero
        fmv.s.x f15, zero
        fmv.s.x f16, zero
        fmv.s.x f17, zero
        fmv.s.x f18, zero
        fmv.s.x f19, zero
        fmv.s.x f20, zero
        fmv.s.x f21, zero
        fmv.s.x f22, zero
        fmv.s.x f23, zero
        fmv.s.x f24, zero
        fmv.s.x f25, zero
        fmv.s.x f26, zero
        fmv.s.x f27, zero
        fmv.s.x f28, zero
        fmv.s.x f29, zero
        fmv.s.x f30, zero
        fmv.s.x f31, zero
        csrw    fcsr, 0
        /* note that the caller must clear SR_FS */
.Lreset_regs_done_fpu:
#endif /* CONFIG_FPU */

#ifdef CONFIG_RISCV_ISA_V
        csrr    t0, CSR_MISA
        li      t1, COMPAT_HWCAP_ISA_V
        and     t0, t0, t1
        beqz    t0, .Lreset_regs_done_vector

        /*
         * Clear vector registers and reset vcsr
         * VLMAX has a defined value, VLEN is a constant,
         * and this form of vsetvli is defined to set vl to VLMAX.
         */
        li      t1, SR_VS
        csrs    CSR_STATUS, t1
        csrs    CSR_VCSR, x0
        vsetvli t1, x0, e8, m8, ta, ma
        vmv.v.i v0, 0
        vmv.v.i v8, 0
        vmv.v.i v16, 0
        vmv.v.i v24, 0
        /* note that the caller must clear SR_VS */
.Lreset_regs_done_vector:
#endif /* CONFIG_RISCV_ISA_V */
        ret
SYM_CODE_END(reset_regs)
#endif /* CONFIG_RISCV_M_MODE */