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* Low-level CPU initialisation
* Based on arch/arm/kernel/head.S
* Copyright (C) 1994-2002 Russell King
* Copyright (C) 2003-2012 ARM Ltd.
* Authors: Catalin Marinas <>
* Will Deacon <>
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <>.
#include <linux/linkage.h>
#include <linux/init.h>
#include <linux/irqchip/arm-gic-v3.h>
#include <asm/assembler.h>
#include <asm/ptrace.h>
#include <asm/asm-offsets.h>
#include <asm/cache.h>
#include <asm/cputype.h>
#include <asm/kernel-pgtable.h>
#include <asm/kvm_arm.h>
#include <asm/memory.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable.h>
#include <asm/page.h>
#include <asm/sysreg.h>
#include <asm/thread_info.h>
#include <asm/virt.h>
#if (TEXT_OFFSET & 0xfff) != 0
#error TEXT_OFFSET must be at least 4KB aligned
#elif (PAGE_OFFSET & 0x1fffff) != 0
#error PAGE_OFFSET must be at least 2MB aligned
#elif TEXT_OFFSET > 0x1fffff
#error TEXT_OFFSET must be less than 2MB
#define KERNEL_START _text
#define KERNEL_END _end
* Kernel startup entry point.
* ---------------------------
* The requirements are:
* MMU = off, D-cache = off, I-cache = on or off,
* x0 = physical address to the FDT blob.
* This code is mostly position independent so you call this at
* Note that the callee-saved registers are used for storing variables
* that are useful before the MMU is enabled. The allocations are described
* in the entry routines.
* DO NOT MODIFY. Image header expected by Linux boot-loaders.
* This add instruction has no meaningful effect except that
* its opcode forms the magic "MZ" signature required by UEFI.
add x13, x18, #0x16
b stext
b stext // branch to kernel start, magic
.long 0 // reserved
.quad _kernel_offset_le // Image load offset from start of RAM, little-endian
.quad _kernel_size_le // Effective size of kernel image, little-endian
.quad _kernel_flags_le // Informative flags, little-endian
.quad 0 // reserved
.quad 0 // reserved
.quad 0 // reserved
.byte 0x41 // Magic number, "ARM\x64"
.byte 0x52
.byte 0x4d
.byte 0x64
.long pe_header - efi_head // Offset to the PE header.
.word 0 // reserved
.globl __efistub_stext_offset
.set __efistub_stext_offset, stext - efi_head
.align 3
.ascii "PE"
.short 0
.short 0xaa64 // AArch64
.short 2 // nr_sections
.long 0 // TimeDateStamp
.long 0 // PointerToSymbolTable
.long 1 // NumberOfSymbols
.short section_table - optional_header // SizeOfOptionalHeader
.short 0x206 // Characteristics.
.short 0x20b // PE32+ format
.byte 0x02 // MajorLinkerVersion
.byte 0x14 // MinorLinkerVersion
.long _end - stext // SizeOfCode
.long 0 // SizeOfInitializedData
.long 0 // SizeOfUninitializedData
.long __efistub_entry - efi_head // AddressOfEntryPoint
.long __efistub_stext_offset // BaseOfCode
.quad 0 // ImageBase
.long 0x1000 // SectionAlignment
.long PECOFF_FILE_ALIGNMENT // FileAlignment
.short 0 // MajorOperatingSystemVersion
.short 0 // MinorOperatingSystemVersion
.short 0 // MajorImageVersion
.short 0 // MinorImageVersion
.short 0 // MajorSubsystemVersion
.short 0 // MinorSubsystemVersion
.long 0 // Win32VersionValue
.long _end - efi_head // SizeOfImage
// Everything before the kernel image is considered part of the header
.long __efistub_stext_offset // SizeOfHeaders
.long 0 // CheckSum
.short 0xa // Subsystem (EFI application)
.short 0 // DllCharacteristics
.quad 0 // SizeOfStackReserve
.quad 0 // SizeOfStackCommit
.quad 0 // SizeOfHeapReserve
.quad 0 // SizeOfHeapCommit
.long 0 // LoaderFlags
.long 0x6 // NumberOfRvaAndSizes
.quad 0 // ExportTable
.quad 0 // ImportTable
.quad 0 // ResourceTable
.quad 0 // ExceptionTable
.quad 0 // CertificationTable
.quad 0 // BaseRelocationTable
// Section table
* The EFI application loader requires a relocation section
* because EFI applications must be relocatable. This is a
* dummy section as far as we are concerned.
.ascii ".reloc"
.byte 0
.byte 0 // end of 0 padding of section name
.long 0
.long 0
.long 0 // SizeOfRawData
.long 0 // PointerToRawData
.long 0 // PointerToRelocations
.long 0 // PointerToLineNumbers
.short 0 // NumberOfRelocations
.short 0 // NumberOfLineNumbers
.long 0x42100040 // Characteristics (section flags)
.ascii ".text"
.byte 0
.byte 0
.byte 0 // end of 0 padding of section name
.long _end - stext // VirtualSize
.long __efistub_stext_offset // VirtualAddress
.long _edata - stext // SizeOfRawData
.long __efistub_stext_offset // PointerToRawData
.long 0 // PointerToRelocations (0 for executables)
.long 0 // PointerToLineNumbers (0 for executables)
.short 0 // NumberOfRelocations (0 for executables)
.short 0 // NumberOfLineNumbers (0 for executables)
.long 0xe0500020 // Characteristics (section flags)
* EFI will load stext onwards at the 4k section alignment
* described in the PE/COFF header. To ensure that instruction
* sequences using an adrp and a :lo12: immediate will function
* correctly at this alignment, we must ensure that stext is
* placed at a 4k boundary in the Image to begin with.
.align 12
bl preserve_boot_args
bl el2_setup // Drop to EL1, w20=cpu_boot_mode
adrp x24, __PHYS_OFFSET
bl set_cpu_boot_mode_flag
bl __create_page_tables // x25=TTBR0, x26=TTBR1
* The following calls CPU setup code, see arch/arm64/mm/proc.S for
* details.
* On return, the CPU will be ready for the MMU to be turned on and
* the TCR will have been set.
ldr x27, =__mmap_switched // address to jump to after
// MMU has been enabled
adr_l lr, __enable_mmu // return (PIC) address
b __cpu_setup // initialise processor
* Preserve the arguments passed by the bootloader in x0 .. x3
mov x21, x0 // x21=FDT
adr_l x0, boot_args // record the contents of
stp x21, x1, [x0] // x0 .. x3 at kernel entry
stp x2, x3, [x0, #16]
dmb sy // needed before dc ivac with
// MMU off
add x1, x0, #0x20 // 4 x 8 bytes
b __inval_cache_range // tail call
* Macro to create a table entry to the next page.
* tbl: page table address
* virt: virtual address
* shift: #imm page table shift
* ptrs: #imm pointers per table page
* Preserves: virt
* Corrupts: tmp1, tmp2
* Returns: tbl -> next level table page address
.macro create_table_entry, tbl, virt, shift, ptrs, tmp1, tmp2
lsr \tmp1, \virt, #\shift
and \tmp1, \tmp1, #\ptrs - 1 // table index
add \tmp2, \tbl, #PAGE_SIZE
orr \tmp2, \tmp2, #PMD_TYPE_TABLE // address of next table and entry type
str \tmp2, [\tbl, \tmp1, lsl #3]
add \tbl, \tbl, #PAGE_SIZE // next level table page
* Macro to populate the PGD (and possibily PUD) for the corresponding
* block entry in the next level (tbl) for the given virtual address.
* Preserves: tbl, next, virt
* Corrupts: tmp1, tmp2
.macro create_pgd_entry, tbl, virt, tmp1, tmp2
create_table_entry \tbl, \virt, PGDIR_SHIFT, PTRS_PER_PGD, \tmp1, \tmp2
create_table_entry \tbl, \virt, PUD_SHIFT, PTRS_PER_PUD, \tmp1, \tmp2
create_table_entry \tbl, \virt, SWAPPER_TABLE_SHIFT, PTRS_PER_PTE, \tmp1, \tmp2
* Macro to populate block entries in the page table for the start..end
* virtual range (inclusive).
* Preserves: tbl, flags
* Corrupts: phys, start, end, pstate
.macro create_block_map, tbl, flags, phys, start, end
lsr \phys, \phys, #SWAPPER_BLOCK_SHIFT
lsr \start, \start, #SWAPPER_BLOCK_SHIFT
and \start, \start, #PTRS_PER_PTE - 1 // table index
orr \phys, \flags, \phys, lsl #SWAPPER_BLOCK_SHIFT // table entry
lsr \end, \end, #SWAPPER_BLOCK_SHIFT
and \end, \end, #PTRS_PER_PTE - 1 // table end index
9999: str \phys, [\tbl, \start, lsl #3] // store the entry
add \start, \start, #1 // next entry
add \phys, \phys, #SWAPPER_BLOCK_SIZE // next block
cmp \start, \end 9999b
* Setup the initial page tables. We only setup the barest amount which is
* required to get the kernel running. The following sections are required:
* - identity mapping to enable the MMU (low address, TTBR0)
* - first few MB of the kernel linear mapping to jump to once the MMU has
* been enabled
adrp x25, idmap_pg_dir
adrp x26, swapper_pg_dir
mov x27, lr
* Invalidate the idmap and swapper page tables to avoid potential
* dirty cache lines being evicted.
mov x0, x25
add x1, x26, #SWAPPER_DIR_SIZE
bl __inval_cache_range
* Clear the idmap and swapper page tables.
mov x0, x25
add x6, x26, #SWAPPER_DIR_SIZE
1: stp xzr, xzr, [x0], #16
stp xzr, xzr, [x0], #16
stp xzr, xzr, [x0], #16
stp xzr, xzr, [x0], #16
cmp x0, x6
b.lo 1b
* Create the identity mapping.
mov x0, x25 // idmap_pg_dir
adrp x3, __idmap_text_start // __pa(__idmap_text_start)
#ifndef CONFIG_ARM64_VA_BITS_48
#define EXTRA_PTRS (1 << (48 - EXTRA_SHIFT))
* If VA_BITS < 48, it may be too small to allow for an ID mapping to be
* created that covers system RAM if that is located sufficiently high
* in the physical address space. So for the ID map, use an extended
* virtual range in that case, by configuring an additional translation
* level.
* First, we have to verify our assumption that the current value of
* VA_BITS was chosen such that all translation levels are fully
* utilised, and that lowering T0SZ will always result in an additional
* translation level to be configured.
#error "Mismatch between VA_BITS and page size/number of translation levels"
* Calculate the maximum allowed value for TCR_EL1.T0SZ so that the
* entire ID map region can be mapped. As T0SZ == (64 - #bits used),
* this number conveniently equals the number of leading zeroes in
* the physical address of __idmap_text_end.
adrp x5, __idmap_text_end
clz x5, x5
cmp x5, TCR_T0SZ(VA_BITS) // default T0SZ small enough? 1f // .. then skip additional level
adr_l x6, idmap_t0sz
str x5, [x6]
dmb sy
dc ivac, x6 // Invalidate potentially stale cache line
create_table_entry x0, x3, EXTRA_SHIFT, EXTRA_PTRS, x5, x6
create_pgd_entry x0, x3, x5, x6
mov x5, x3 // __pa(__idmap_text_start)
adr_l x6, __idmap_text_end // __pa(__idmap_text_end)
create_block_map x0, x7, x3, x5, x6
* Map the kernel image (starting with PHYS_OFFSET).
mov x0, x26 // swapper_pg_dir
mov x5, #PAGE_OFFSET
create_pgd_entry x0, x5, x3, x6
ldr x6, =KERNEL_END // __va(KERNEL_END)
mov x3, x24 // phys offset
create_block_map x0, x7, x3, x5, x6
* Since the page tables have been populated with non-cacheable
* accesses (MMU disabled), invalidate the idmap and swapper page
* tables again to remove any speculatively loaded cache lines.
mov x0, x25
add x1, x26, #SWAPPER_DIR_SIZE
dmb sy
bl __inval_cache_range
mov lr, x27
* The following fragment of code is executed with the MMU enabled.
.set initial_sp, init_thread_union + THREAD_START_SP
adr_l x6, __bss_start
adr_l x7, __bss_stop
1: cmp x6, x7
b.hs 2f
str xzr, [x6], #8 // Clear BSS
b 1b
adr_l sp, initial_sp, x4
str_l x21, __fdt_pointer, x5 // Save FDT pointer
str_l x24, memstart_addr, x6 // Save PHYS_OFFSET
mov x29, #0
bl kasan_early_init
b start_kernel
* end early head section, begin head code that is also used for
* hotplug and needs to have the same protections as the text region
.section ".text","ax"
* If we're fortunate enough to boot at EL2, ensure that the world is
* sane before dropping to EL1.
* Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in x20 if
* booted in EL1 or EL2 respectively.
msr SPsel, #1 // We want to use SP_EL{1,2}
mrs x0, CurrentEL
cmp x0, #CurrentEL_EL2 1f
mrs x0, sctlr_el2
CPU_BE( orr x0, x0, #(1 << 25) ) // Set the EE bit for EL2
CPU_LE( bic x0, x0, #(1 << 25) ) // Clear the EE bit for EL2
msr sctlr_el2, x0
b 2f
1: mrs x0, sctlr_el1
CPU_BE( orr x0, x0, #(3 << 24) ) // Set the EE and E0E bits for EL1
CPU_LE( bic x0, x0, #(3 << 24) ) // Clear the EE and E0E bits for EL1
msr sctlr_el1, x0
mov w20, #BOOT_CPU_MODE_EL1 // This cpu booted in EL1
/* Hyp configuration. */
2: mov_q x0, HCR_HOST_NVHE_FLAGS
msr hcr_el2, x0
/* Generic timers. */
mrs x0, cnthctl_el2
orr x0, x0, #3 // Enable EL1 physical timers
msr cnthctl_el2, x0
msr cntvoff_el2, xzr // Clear virtual offset
/* GICv3 system register access */
mrs x0, id_aa64pfr0_el1
ubfx x0, x0, #24, #4
cbz x0, 3f
mrs_s x0, ICC_SRE_EL2
orr x0, x0, #ICC_SRE_EL2_SRE // Set ICC_SRE_EL2.SRE==1
orr x0, x0, #ICC_SRE_EL2_ENABLE // Set ICC_SRE_EL2.Enable==1
msr_s ICC_SRE_EL2, x0
isb // Make sure SRE is now set
mrs_s x0, ICC_SRE_EL2 // Read SRE back,
tbz x0, #0, 3f // and check that it sticks
msr_s ICH_HCR_EL2, xzr // Reset ICC_HCR_EL2 to defaults
/* Populate ID registers. */
mrs x0, midr_el1
mrs x1, mpidr_el1
msr vpidr_el2, x0
msr vmpidr_el2, x1
/* sctlr_el1 */
mov x0, #0x0800 // Set/clear RES{1,0} bits
CPU_BE( movk x0, #0x33d0, lsl #16 ) // Set EE and E0E on BE systems
CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems
msr sctlr_el1, x0
/* Coprocessor traps. */
mov x0, #0x33ff
msr cptr_el2, x0 // Disable copro. traps to EL2
msr hstr_el2, xzr // Disable CP15 traps to EL2
/* EL2 debug */
mrs x0, id_aa64dfr0_el1 // Check ID_AA64DFR0_EL1 PMUVer
sbfx x0, x0, #8, #4
cmp x0, #1 4f // Skip if no PMU present
mrs x0, pmcr_el0 // Disable debug access traps
ubfx x0, x0, #11, #5 // to EL2 and allow access to
csel x0, xzr, x0, lt // all PMU counters from EL1
msr mdcr_el2, x0 // (if they exist)
/* Stage-2 translation */
msr vttbr_el2, xzr
/* Hypervisor stub */
adrp x0, __hyp_stub_vectors
add x0, x0, #:lo12:__hyp_stub_vectors
msr vbar_el2, x0
/* spsr */
mov x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
msr spsr_el2, x0
msr elr_el2, lr
mov w20, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
* Sets the __boot_cpu_mode flag depending on the CPU boot mode passed
* in x20. See arch/arm64/include/asm/virt.h for more info.
adr_l x1, __boot_cpu_mode
cmp w20, #BOOT_CPU_MODE_EL2 1f
add x1, x1, #4
1: str w20, [x1] // This CPU has booted in EL1
dmb sy
dc ivac, x1 // Invalidate potentially stale cache line
* We need to find out the CPU boot mode long after boot, so we need to
* store it in a writable variable.
* This is not in .bss, because we set it sufficiently early that the boot-time
* zeroing of .bss would clobber it.
.pushsection .data..cacheline_aligned
* This provides a "holding pen" for platforms to hold all secondary
* cores are held until we're ready for them to initialise.
bl el2_setup // Drop to EL1, w20=cpu_boot_mode
bl set_cpu_boot_mode_flag
mrs x0, mpidr_el1
and x0, x0, x1
adr_l x3, secondary_holding_pen_release
pen: ldr x4, [x3]
cmp x4, x0
b.eq secondary_startup
b pen
* Secondary entry point that jumps straight into the kernel. Only to
* be used where CPUs are brought online dynamically by the kernel.
bl el2_setup // Drop to EL1
bl set_cpu_boot_mode_flag
b secondary_startup
* Common entry point for secondary CPUs.
adrp x25, idmap_pg_dir
adrp x26, swapper_pg_dir
bl __cpu_setup // initialise processor
ldr x21, =secondary_data
ldr x27, =__secondary_switched // address to jump to after enabling the MMU
b __enable_mmu
ldr x0, [x21] // get secondary_data.stack
mov sp, x0
mov x29, #0
b secondary_start_kernel
* Enable the MMU.
* x0 = SCTLR_EL1 value for turning on the MMU.
* x27 = *virtual* address to jump to upon completion
* Other registers depend on the function called upon completion.
* Checks if the selected granule size is supported by the CPU.
* If it isn't, park the CPU
.section ".idmap.text", "ax"
mrs x1, ID_AA64MMFR0_EL1
ubfx x2, x1, #ID_AA64MMFR0_TGRAN_SHIFT, 4
cmp x2, #ID_AA64MMFR0_TGRAN_SUPPORTED __no_granule_support
ldr x5, =vectors
msr vbar_el1, x5
msr ttbr0_el1, x25 // load TTBR0
msr ttbr1_el1, x26 // load TTBR1
msr sctlr_el1, x0
* Invalidate the local I-cache so that any instructions fetched
* speculatively from the PoC are discarded, since they may have
* been dynamically patched at the PoU.
ic iallu
dsb nsh
br x27
b __no_granule_support