Re: [PATCH v3] RISC-V: enable XIP

From: Anup Patel
Date: Tue Dec 22 2020 - 00:20:29 EST

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On Tue, Dec 22, 2020 at 2:08 AM Vitaly Wool <vitaly.wool@xxxxxxxxxxxx> wrote:
>
> Introduce XIP (eXecute In Place) support for RISC-V platforms.
> It allows code to be executed directly from non-volatile storage
> directly addressable by the CPU, such as QSPI NOR flash which can
> be found on many RISC-V platforms. This makes way for significant
> optimization of RAM footprint. The XIP kernel is not compressed
> since it has to run directly from flash, so it will occupy more
> space on the non-volatile storage to The physical flash address
> used to link the kernel object files and for storing it has to
> be known at compile time and is represented by a Kconfig option.
>
> XIP on RISC-V will currently only work on MMU-enabled kernels.
>
> Changed in v2:
> - dedicated macro for XIP address fixup when MMU is not enabled yet
> o both for 32-bit and 64-bit RISC-V
> - SP is explicitly set to a safe place in RAM before __copy_data call
> - removed redundant alignment requirements in vmlinux-xip.lds.S
> - changed long -> uintptr_t typecast in __XIP_FIXUP macro.
>
> Changed in v3:
> - rebased against latest for-next
> - XIP address fixup macro now takes an argument
> - SMP related fixes
> Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
> ---
> arch/riscv/Kconfig | 46 ++++++++-
> arch/riscv/Makefile | 8 +-
> arch/riscv/boot/Makefile | 13 +++
> arch/riscv/include/asm/pgtable.h | 56 +++++++++--
> arch/riscv/kernel/cpu_ops_sbi.c | 3 +
> arch/riscv/kernel/head.S | 69 +++++++++++++-
> arch/riscv/kernel/head.h | 3 +
> arch/riscv/kernel/setup.c | 8 +-
> arch/riscv/kernel/vmlinux-xip.lds.S | 132 ++++++++++++++++++++++++++
> arch/riscv/kernel/vmlinux.lds.S | 6 ++
> arch/riscv/mm/init.c | 142 +++++++++++++++++++++++++---
> 11 files changed, 460 insertions(+), 26 deletions(-)
> create mode 100644 arch/riscv/kernel/vmlinux-xip.lds.S

If possible please break down this patch into smaller patches
which are bisect-able and easy to reivew.

>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 2b41f6d8e458..fabafdf763da 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -398,7 +398,7 @@ config EFI_STUB
>
> config EFI
> bool "UEFI runtime support"
> - depends on OF
> + depends on OF && !XIP_KERNEL
> select LIBFDT
> select UCS2_STRING
> select EFI_PARAMS_FROM_FDT
> @@ -415,12 +415,52 @@ config EFI
> allow the kernel to be booted as an EFI application. This
> is only useful on systems that have UEFI firmware.
>
> +config XIP_KERNEL
> + bool "Kernel Execute-In-Place from ROM"
> + depends on MMU
> + help
> + Execute-In-Place allows the kernel to run from non-volatile storage
> + directly addressable by the CPU, such as NOR flash. This saves RAM
> + space since the text section of the kernel is not loaded from flash
> + to RAM. Read-write sections, such as the data section and stack,
> + are still copied to RAM. The XIP kernel is not compressed since
> + it has to run directly from flash, so it will take more space to
> + store it. The flash address used to link the kernel object files,
> + and for storing it, is configuration dependent. Therefore, if you
> + say Y here, you must know the proper physical address where to
> + store the kernel image depending on your own flash memory usage.
> +
> + Also note that the make target becomes "make xipImage" rather than
> + "make zImage" or "make Image". The final kernel binary to put in
> + ROM memory will be arch/riscv/boot/xipImage.
> +
> + If unsure, say N.
> +
> +config XIP_PHYS_ADDR
> + hex "XIP Kernel Physical Location"
> + depends on XIP_KERNEL
> + default "0x21000000"
> + help
> + This is the physical address in your flash memory the kernel will
> + be linked for and stored to. This address is dependent on your
> + own flash usage.
> +
> +config XIP_PHYS_RAM_BASE
> + hex "Platform Physical RAM address"
> + depends on XIP_KERNEL
> + default "0x80000000"
> + help
> + This is the physical address of RAM in the system. It has to be
> + explicitly specified to run early relocations of read-write data
> + from flash to RAM.
> endmenu
>
> config BUILTIN_DTB
> - def_bool n
> - depends on RISCV_M_MODE
> + bool
> + depends on (RISCV_M_MODE || XIP_KERNEL)
> depends on OF
> + default y if XIP_KERNEL
> + default n if !XIP_KERNEL

The "default n" case is not required because by default it is disabled.

>
> menu "Power management options"
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 8c29e553ef7f..b89b6897b0be 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -70,7 +70,11 @@ CHECKFLAGS += -D__riscv -D__riscv_xlen=$(BITS)
>
> # Default target when executing plain make
> boot := arch/riscv/boot
> +ifeq ($(CONFIG_XIP_KERNEL),y)
> +KBUILD_IMAGE := $(boot)/xipImage
> +else
> KBUILD_IMAGE := $(boot)/Image.gz
> +endif
>
> head-y := arch/riscv/kernel/head.o
>
> @@ -83,12 +87,14 @@ PHONY += vdso_install
> vdso_install:
> $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
>
> +ifneq ($(CONFIG_XIP_KERNEL),y)
> ifeq ($(CONFIG_RISCV_M_MODE)$(CONFIG_SOC_KENDRYTE),yy)
> KBUILD_IMAGE := $(boot)/loader.bin
> else
> KBUILD_IMAGE := $(boot)/Image.gz
> endif
> -BOOT_TARGETS := Image Image.gz loader loader.bin
> +endif
> +BOOT_TARGETS := Image Image.gz loader loader.bin xipImage
>
> all: $(notdir $(KBUILD_IMAGE))
>
> diff --git a/arch/riscv/boot/Makefile b/arch/riscv/boot/Makefile
> index 03404c84f971..6bf299f70c27 100644
> --- a/arch/riscv/boot/Makefile
> +++ b/arch/riscv/boot/Makefile
> @@ -17,8 +17,21 @@
> KCOV_INSTRUMENT := n
>
> OBJCOPYFLAGS_Image :=-O binary -R .note -R .note.gnu.build-id -R .comment -S
> +OBJCOPYFLAGS_xipImage :=-O binary -R .note -R .note.gnu.build-id -R .comment -S
>
> targets := Image Image.* loader loader.o loader.lds loader.bin
> +targets := Image Image.* loader loader.o loader.lds loader.bin xipImage
> +
> +ifeq ($(CONFIG_XIP_KERNEL),y)
> +
> +quiet_cmd_mkxip = $(quiet_cmd_objcopy)
> +cmd_mkxip = $(cmd_objcopy)
> +
> +$(obj)/xipImage: vmlinux FORCE
> + $(call if_changed,mkxip)
> + @$(kecho) ' Physical Address of xipImage: $(CONFIG_XIP_PHYS_ADDR)'
> +
> +endif
>
> $(obj)/Image: vmlinux FORCE
> $(call if_changed,objcopy)
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 183f1f4b2ae6..ec3360363b71 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -11,6 +11,42 @@
>
> #include <asm/pgtable-bits.h>
>
> +#ifdef CONFIG_MMU
> +
> +#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> +#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> +
> +#ifdef CONFIG_XIP_KERNEL
> +/*
> + * Since we use sections to map it, this macro replaces the physical address
> + * with its virtual address while keeping offset from the base section.
> + */
> +#define XIP_OFFSET SZ_8M
> +#define XIP_MASK (SZ_8M - 1)
> +#define XIP_VIRT_ADDR(physaddr) (PAGE_OFFSET - XIP_OFFSET + ((physaddr) & XIP_MASK))
> +#define XIP_PHYS_ADDR(va) \
> + ((uintptr_t)(va) - PAGE_OFFSET + XIP_OFFSET + CONFIG_XIP_PHYS_ADDR)
> +#define VMALLOC_END (PAGE_OFFSET - SZ_16M - 1)
> +
> +#define XIP_VIRT_ADDR_START XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
> +#define __PHYS_RAM_BASE CONFIG_XIP_PHYS_RAM_BASE
> +
> +#define __XIP_FIXUP(addr) \
> + (((uintptr_t)(addr) >= CONFIG_XIP_PHYS_ADDR && \
> + (uintptr_t)(addr) <= CONFIG_XIP_PHYS_ADDR + SZ_16M) ? \
> + (uintptr_t)(addr) - CONFIG_XIP_PHYS_ADDR + __PHYS_RAM_BASE - XIP_OFFSET : \
> + (uintptr_t)(addr))
> +
> +#else
> +#define VMALLOC_END (PAGE_OFFSET - 1)
> +#endif /* CONFIG_XIP_KERNEL */
> +
> +#else
> +
> +#define XIP_VIRT_ADDR(physaddr) physaddr
> +
> +#endif /* CONFIG_MMU */
> +

Lot of defines above will not work for assembly sources.

Keep only assembly friendly defines outside "#ifndef __ASSEMBLY__"

> #ifndef __ASSEMBLY__
>
> /* Page Upper Directory not used in RISC-V */
> @@ -21,10 +57,6 @@
>
> #ifdef CONFIG_MMU
>
> -#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> -#define VMALLOC_END (PAGE_OFFSET - 1)
> -#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> -
> #define BPF_JIT_REGION_SIZE (SZ_128M)
> #define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE)
> #define BPF_JIT_REGION_END (VMALLOC_END)
> @@ -467,8 +499,20 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl
>
> #define kern_addr_valid(addr) (1) /* FIXME */
>
> -extern void *dtb_early_va;
> -extern uintptr_t dtb_early_pa;
> +extern void *_dtb_early_va;
> +extern uintptr_t _dtb_early_pa;
> +#if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_MMU)
> +
> +#define dtb_early_va (*(void **)__XIP_FIXUP(&_dtb_early_va))
> +#define dtb_early_pa (*(uintptr_t *)__XIP_FIXUP(&_dtb_early_pa))
> +
> +#else
> +
> +#define dtb_early_va _dtb_early_va
> +#define dtb_early_pa _dtb_early_pa
> +
> +#endif /* CONFIG_XIP_KERNEL */
> +
> void setup_bootmem(void);
> void paging_init(void);
>
> diff --git a/arch/riscv/kernel/cpu_ops_sbi.c b/arch/riscv/kernel/cpu_ops_sbi.c
> index 685fae72b7f5..9c8d6dab55b8 100644
> --- a/arch/riscv/kernel/cpu_ops_sbi.c
> +++ b/arch/riscv/kernel/cpu_ops_sbi.c
> @@ -59,6 +59,9 @@ static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
> unsigned long boot_addr = __pa_symbol(secondary_start_sbi);
> int hartid = cpuid_to_hartid_map(cpuid);
>
> +#ifdef CONFIG_XIP_KERNEL
> + boot_addr = XIP_PHYS_ADDR(secondary_start_sbi);
> +#endif

You can avoid "#ifdef CONFIG_XIP_KERNEL" here by defining
XIP_PHYS_ADDR() to do nothing when XIP_KERNEL is disabled.

> cpu_update_secondary_bootdata(cpuid, tidle);
> rc = sbi_hsm_hart_start(hartid, boot_addr, 0);
>
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 45dbdae930bf..6f065a5502d3 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -9,11 +9,31 @@
> #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 "efi-header.S"
>
> +#ifdef CONFIG_XIP_KERNEL
> +.macro XIP_FIXUP_OFFSET reg
> +#ifdef CONFIG_64BIT
> + ld t0, _xip_fixup
> +#else
> + lw t0, _xip_fixup
> +#endif
> + add \reg, \reg, t0
> +.endm
> +
> +_xip_fixup:
> +#ifdef CONFIG_64BIT
> + .dword CONFIG_XIP_PHYS_RAM_BASE - CONFIG_XIP_PHYS_ADDR - XIP_OFFSET
> +#else
> + .word CONFIG_XIP_PHYS_RAM_BASE - CONFIG_XIP_PHYS_ADDR - XIP_OFFSET
> +#endif
> +
> +#endif /* CONFIG_XIP_KERNEL */
> +
> __HEAD
> ENTRY(_start)
> /*
> @@ -64,7 +84,11 @@ pe_head_start:
> #ifdef CONFIG_MMU
> relocate:
> /* Relocate return address */
> +#ifdef CONFIG_XIP_KERNEL
> + li a1, XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
> +#else
> li a1, PAGE_OFFSET
> +#endif
> la a2, _start
> sub a1, a1, a2
> add ra, ra, a1
> @@ -85,7 +109,12 @@ relocate:
> * full fence here because setup_vm() just wrote these PTEs and we need
> * to ensure the new translations are in use.
> */
> +#ifdef CONFIG_XIP_KERNEL
> + la a0, _trampoline_pg_dir
> + XIP_FIXUP_OFFSET a0
> +#else
> la a0, trampoline_pg_dir
> +#endif
> srl a0, a0, PAGE_SHIFT
> or a0, a0, a1
> sfence.vma
> @@ -140,6 +169,10 @@ secondary_start_sbi:
> slli a3, a0, LGREG
> la a4, __cpu_up_stack_pointer
> la a5, __cpu_up_task_pointer
> +#ifdef CONFIG_XIP_KERNEL
> + XIP_FIXUP_OFFSET a4
> + XIP_FIXUP_OFFSET a5
> +#endif
> add a4, a3, a4
> add a5, a3, a5
> REG_L sp, (a4)
> @@ -233,10 +266,24 @@ pmp_done:
>
> /* Pick one hart to run the main boot sequence */
> la a3, hart_lottery
> +#ifdef CONFIG_XIP_KERNEL
> + XIP_FIXUP_OFFSET a3
> +#endif
> li a2, 1
> amoadd.w a3, a2, (a3)
> bnez a3, .Lsecondary_start
>
> +#ifdef CONFIG_XIP_KERNEL
> + la sp, _end + THREAD_SIZE
> + XIP_FIXUP_OFFSET sp
> + mv s0, a0
> + call __copy_data
> +
> + /* Restore a0 copy */
> + mv a0, s0
> +#endif
> +
> +#ifndef CONFIG_XIP_KERNEL
> /* Clear BSS for flat non-ELF images */
> la a3, __bss_start
> la a4, __bss_stop
> @@ -246,19 +293,35 @@ clear_bss:
> add a3, a3, RISCV_SZPTR
> blt a3, a4, clear_bss
> clear_bss_done:
> -
> +#endif
> /* Save hart ID and DTB physical address */
> mv s0, a0
> mv s1, a1
> +
> la a2, boot_cpu_hartid
> +#ifdef CONFIG_XIP_KERNEL
> + XIP_FIXUP_OFFSET a2
> +#endif
> REG_S a0, (a2)
>
> /* Initialize page tables and relocate to virtual addresses */
> la sp, init_thread_union + THREAD_SIZE
> +#ifdef CONFIG_XIP_KERNEL
> + XIP_FIXUP_OFFSET sp
> +#endif
> +#if defined (CONFIG_XIP_KERNEL) && defined (CONFIG_BUILTIN_DTB)
> + la a0, __dtb_start
> +#else
> mv a0, s1
> +#endif
> call setup_vm
> #ifdef CONFIG_MMU
> +#ifdef CONFIG_XIP_KERNEL
> + la a0, _early_pg_dir
> + XIP_FIXUP_OFFSET a0
> +#else
> la a0, early_pg_dir
> +#endif
> call relocate
> #endif /* CONFIG_MMU */
>
> @@ -284,6 +347,10 @@ clear_bss_done:
> slli a3, a0, LGREG
> la a1, __cpu_up_stack_pointer
> la a2, __cpu_up_task_pointer
> +#ifdef CONFIG_XIP_KERNEL
> + XIP_FIXUP_OFFSET a1
> + XIP_FIXUP_OFFSET a2
> +#endif
> add a1, a3, a1
> add a2, a3, a2
>
> diff --git a/arch/riscv/kernel/head.h b/arch/riscv/kernel/head.h
> index b48dda3d04f6..aabbc3ac3e48 100644
> --- a/arch/riscv/kernel/head.h
> +++ b/arch/riscv/kernel/head.h
> @@ -12,6 +12,9 @@ extern atomic_t hart_lottery;
>
> asmlinkage void do_page_fault(struct pt_regs *regs);
> asmlinkage void __init setup_vm(uintptr_t dtb_pa);
> +#ifdef CONFIG_XIP_KERNEL
> +asmlinkage void __init __copy_data(void);
> +#endif
>
> extern void *__cpu_up_stack_pointer[];
> extern void *__cpu_up_task_pointer[];
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index a834deab31d3..876d4ff0ecc4 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -50,7 +50,11 @@ struct screen_info screen_info __section(".data") = {
> * This is used before the kernel initializes the BSS so it can't be in the
> * BSS.
> */
> -atomic_t hart_lottery __section(".sdata");
> +atomic_t hart_lottery __section(".sdata")
> +#ifdef CONFIG_XIP_KERNEL
> += ATOMIC_INIT(1)
> +#endif
> +;
> unsigned long boot_cpu_hartid;
> static DEFINE_PER_CPU(struct cpu, cpu_devices);
>
> @@ -244,7 +248,7 @@ void __init setup_arch(char **cmdline_p)
> #if IS_ENABLED(CONFIG_BUILTIN_DTB)
> unflatten_and_copy_device_tree();
> #else
> - if (early_init_dt_verify(__va(dtb_early_pa)))
> + if (early_init_dt_verify(dtb_early_va))

We can't use dtb_early_va here because early DTB mappings are only done
in early_pg_dir but not available in swapper_pg_dir.

> unflatten_device_tree();
> else
> pr_err("No DTB found in kernel mappings\n");
> diff --git a/arch/riscv/kernel/vmlinux-xip.lds.S b/arch/riscv/kernel/vmlinux-xip.lds.S
> new file mode 100644
> index 000000000000..9f0f08c34cd3
> --- /dev/null
> +++ b/arch/riscv/kernel/vmlinux-xip.lds.S
> @@ -0,0 +1,132 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2012 Regents of the University of California
> + * Copyright (C) 2017 SiFive
> + * Copyright (C) 2020 Vitaly Wool, Konsulko AB
> + */
> +
> +#define LOAD_OFFSET XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
> +/* No __ro_after_init data in the .rodata section - which will always be ro */
> +#define RO_AFTER_INIT_DATA
> +
> +#include <asm/vmlinux.lds.h>
> +#include <asm/page.h>
> +#include <asm/pgtable.h>
> +#include <asm/cache.h>
> +#include <asm/thread_info.h>
> +
> +OUTPUT_ARCH(riscv)
> +ENTRY(_start)
> +
> +jiffies = jiffies_64;
> +
> +SECTIONS
> +{
> + /* Beginning of code and text segment */
> + . = XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR);
> + _xiprom = .;
> + _start = .;
> + HEAD_TEXT_SECTION
> + INIT_TEXT_SECTION(PAGE_SIZE)
> + /* we have to discard exit text and such at runtime, not link time */
> + .exit.text :
> + {
> + EXIT_TEXT
> + }
> +
> + .text : {
> + _text = .;
> + _stext = .;
> + TEXT_TEXT
> + SCHED_TEXT
> + CPUIDLE_TEXT
> + LOCK_TEXT
> + KPROBES_TEXT
> + ENTRY_TEXT
> + IRQENTRY_TEXT
> + SOFTIRQENTRY_TEXT
> + *(.fixup)
> + _etext = .;
> + }
> + RO_DATA(L1_CACHE_BYTES)
> + .srodata : {
> + *(.srodata*)
> + }
> + .init.rodata : {
> + INIT_SETUP(16)
> + INIT_CALLS
> + CON_INITCALL
> + INIT_RAM_FS
> + }
> + _exiprom = .; /* End of XIP ROM area */
> +
> +
> +/*
> + * From this point, stuff is considered writable and will be copied to RAM
> + */
> + __data_loc = ALIGN(16); /* location in file */
> + . = PAGE_OFFSET; /* location in memory */
> +
> + _sdata = .; /* Start of data section */
> + _data = .;
> + RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
> + _edata = .;
> + __start_ro_after_init = .;
> + .data.ro_after_init : AT(ADDR(.data.ro_after_init) - LOAD_OFFSET) {
> + *(.data..ro_after_init)
> + }
> + __end_ro_after_init = .;
> +
> + . = ALIGN(PAGE_SIZE);
> + __init_begin = .;
> + .init.data : {
> + INIT_DATA
> + }
> + .exit.data : {
> + EXIT_DATA
> + }
> + . = ALIGN(8);
> + __soc_early_init_table : {
> + __soc_early_init_table_start = .;
> + KEEP(*(__soc_early_init_table))
> + __soc_early_init_table_end = .;
> + }
> + __soc_builtin_dtb_table : {
> + __soc_builtin_dtb_table_start = .;
> + KEEP(*(__soc_builtin_dtb_table))
> + __soc_builtin_dtb_table_end = .;
> + }
> + PERCPU_SECTION(L1_CACHE_BYTES)
> +
> + . = ALIGN(PAGE_SIZE);
> + __init_end = .;
> +
> + .sdata : {
> + __global_pointer$ = . + 0x800;
> + *(.sdata*)
> + *(.sbss*)
> + }
> +
> + BSS_SECTION(PAGE_SIZE, PAGE_SIZE, 0)
> + EXCEPTION_TABLE(0x10)
> +
> + .rel.dyn : AT(ADDR(.rel.dyn) - LOAD_OFFSET) {
> + *(.rel.dyn*)
> + }
> +
> + /*
> + * End of copied data. We need a dummy section to get its LMA.
> + * Also located before final ALIGN() as trailing padding is not stored
> + * in the resulting binary file and useless to copy.
> + */
> + .data.endmark : AT(ADDR(.data.endmark) - LOAD_OFFSET) { }
> + _edata_loc = LOADADDR(.data.endmark);
> +
> + . = ALIGN(PAGE_SIZE);
> + _end = .;
> +
> + STABS_DEBUG
> + DWARF_DEBUG
> +
> + DISCARDS
> +}

Atish's patch series "[PATCH v3 0/5] Improve kernel section protections"
updates vmlinux.lds.S so take that as reference for your vmlinux-xip.lds.S

> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> index de03cb22d0e9..6745ec325930 100644
> --- a/arch/riscv/kernel/vmlinux.lds.S
> +++ b/arch/riscv/kernel/vmlinux.lds.S
> @@ -4,7 +4,12 @@
> * Copyright (C) 2017 SiFive
> */
>
> +#ifdef CONFIG_XIP_KERNEL
> +#include "vmlinux-xip.lds.S"
> +#else
> +
> #define LOAD_OFFSET PAGE_OFFSET
> +
> #include <asm/vmlinux.lds.h>
> #include <asm/page.h>
> #include <asm/cache.h>
> @@ -132,3 +137,4 @@ SECTIONS
>
> DISCARDS
> }
> +#endif /* CONFIG_XIP_KERNEL */
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 87c305c566ac..8636432400df 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -30,8 +30,8 @@ EXPORT_SYMBOL(empty_zero_page);
>
> extern char _start[];
> #define DTB_EARLY_BASE_VA PGDIR_SIZE
> -void *dtb_early_va __initdata;
> -uintptr_t dtb_early_pa __initdata;
> +void *_dtb_early_va __initdata;
> +uintptr_t _dtb_early_pa __initdata;
>
> struct pt_alloc_ops {
> pte_t *(*get_pte_virt)(phys_addr_t pa);
> @@ -87,6 +87,10 @@ static void print_vm_layout(void)
> (unsigned long)VMALLOC_END);
> print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
> (unsigned long)high_memory);
> +#ifdef CONFIG_XIP_KERNEL
> + print_mlm("xip", (unsigned long)XIP_VIRT_ADDR_START,
> + (unsigned long)XIP_VIRT_ADDR_START + SZ_16M);
> +#endif /* CONFIG_XIP_KERNEL */
> }
> #else
> static void print_vm_layout(void) { }
> @@ -163,6 +167,10 @@ void __init setup_bootmem(void)
> phys_addr_t vmlinux_start = __pa_symbol(&_start);
> u64 i;
>
> +#ifdef CONFIG_XIP_KERNEL
> + vmlinux_start = __pa_symbol(&_sdata);
> +#endif
> +
> /* Find the memory region containing the kernel */
> for_each_mem_range(i, &start, &end) {
> phys_addr_t size = end - start;
> @@ -194,11 +202,18 @@ void __init setup_bootmem(void)
> setup_initrd();
> #endif /* CONFIG_BLK_DEV_INITRD */
>
> - /*
> - * Avoid using early_init_fdt_reserve_self() since __pa() does
> - * not work for DTB pointers that are fixmap addresses
> - */
> - memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> +#ifdef CONFIG_XIP_KERNEL
> + if (dtb_early_pa < CONFIG_XIP_PHYS_ADDR ||
> + dtb_early_pa > CONFIG_XIP_PHYS_ADDR + SZ_16M)
> +#endif
> + {
> + /*
> + * Avoid using early_init_fdt_reserve_self() since __pa() does
> + * not work for DTB pointers that are fixmap addresses
> + */
> + memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> + dtb_early_va = __va(dtb_early_pa);

Drop this "dtb_early_va" assignment.

> + }
>
> early_init_fdt_scan_reserved_mem();
> dma_contiguous_reserve(dma32_phys_limit);
> @@ -206,21 +221,47 @@ void __init setup_bootmem(void)
> memblock_dump_all();
> }
>
> +#ifdef CONFIG_XIP_KERNEL
> +
> +extern char _xiprom[], _exiprom[];
> +extern char _sdata[], _edata[];
> +
> +#endif /* CONFIG_XIP_KERNEL */
> +
> #ifdef CONFIG_MMU
> -static struct pt_alloc_ops pt_ops;
> +static struct pt_alloc_ops _pt_ops;
> +
> +#ifdef CONFIG_XIP_KERNEL
> +#define pt_ops (*(struct pt_alloc_ops *)__XIP_FIXUP(&_pt_ops))
> +#else
> +#define pt_ops _pt_ops
> +#endif
>
> unsigned long va_pa_offset;
> EXPORT_SYMBOL(va_pa_offset);
> +#ifdef CONFIG_XIP_KERNEL
> +#define va_pa_offset (*((unsigned long *)__XIP_FIXUP(&va_pa_offset)))
> +#endif
> unsigned long pfn_base;
> EXPORT_SYMBOL(pfn_base);
>
> pgd_t swapper_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> -pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> -pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
>
> #define MAX_EARLY_MAPPING_SIZE SZ_128M
>
> +#ifdef CONFIG_XIP_KERNEL
> +pgd_t _trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> +pte_t _fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> +pgd_t _early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> +
> +#define trampoline_pg_dir ((pgd_t *)__XIP_FIXUP(_trampoline_pg_dir))
> +#define fixmap_pte ((pte_t *)__XIP_FIXUP(_fixmap_pte))
> +#define early_pg_dir ((pgd_t *)__XIP_FIXUP(_early_pg_dir))
> +#else
> +pgd_t trampoline_pg_dir[PTRS_PER_PGD] __page_aligned_bss;
> +pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
> pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> +#endif /* CONFIG_XIP_KERNEL */
>
> void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
> {
> @@ -292,15 +333,27 @@ static void __init create_pte_mapping(pte_t *ptep,
>
> #ifndef __PAGETABLE_PMD_FOLDED
>
> -pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> -pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> -
> #if MAX_EARLY_MAPPING_SIZE < PGDIR_SIZE
> #define NUM_EARLY_PMDS 1UL
> #else
> #define NUM_EARLY_PMDS (1UL + MAX_EARLY_MAPPING_SIZE / PGDIR_SIZE)
> #endif
> +
> +#ifdef CONFIG_XIP_KERNEL
> +pmd_t _trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +pmd_t _fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +pmd_t _xip_pmd[PTRS_PER_PGD * NUM_EARLY_PMDS] __page_aligned_bss;
> +pmd_t _early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
> +
> +#define trampoline_pmd ((pmd_t *)__XIP_FIXUP(_trampoline_pmd))
> +#define fixmap_pmd ((pmd_t *)__XIP_FIXUP(_fixmap_pmd))
> +#define xip_pmd ((pmd_t *)__XIP_FIXUP(_xip_pmd))
> +#define early_pmd ((pmd_t *)__XIP_FIXUP(_early_pmd))
> +#else
> +pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
> pmd_t early_pmd[PTRS_PER_PMD * NUM_EARLY_PMDS] __initdata __aligned(PAGE_SIZE);
> +#endif
>
> static pmd_t *__init get_pmd_virt_early(phys_addr_t pa)
> {
> @@ -420,6 +473,19 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
> return PMD_SIZE;
> }
>
> +#ifdef CONFIG_XIP_KERNEL
> +/* called from head.S with MMU off */
> +asmlinkage void __init __copy_data(void)
> +{
> + void *from = (void *)(&_sdata);
> + void *end = (void *)(&_end);
> + void *to = (void *)CONFIG_XIP_PHYS_RAM_BASE;
> + size_t sz = (size_t)(end - from);
> +
> + memcpy(to, from, sz);
> +}
> +#endif
> +
> /*
> * setup_vm() is called from head.S with MMU-off.
> *
> @@ -448,6 +514,19 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> pmd_t fix_bmap_spmd, fix_bmap_epmd;
> #endif
>
> +#ifdef CONFIG_XIP_KERNEL
> + uintptr_t xiprom = (uintptr_t)CONFIG_XIP_PHYS_ADDR;
> + uintptr_t xiprom_sz = (uintptr_t)(&_exiprom) - (uintptr_t)(&_xiprom);
> + uintptr_t xip_map_size = best_map_size(xiprom,
> + MAX_EARLY_MAPPING_SIZE);
> +
> + BUG_ON((xiprom % xip_map_size) != 0);
> + BUG_ON(xiprom_sz > MAX_EARLY_MAPPING_SIZE);
> +
> + load_pa = (uintptr_t)CONFIG_XIP_PHYS_RAM_BASE;
> + load_sz = (uintptr_t)(&_end) - (uintptr_t)(&_sdata);
> + map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> +#endif

Add new line here.

> va_pa_offset = PAGE_OFFSET - load_pa;
> pfn_base = PFN_DOWN(load_pa);
>
> @@ -487,6 +566,21 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
> #endif
>
> +#ifdef CONFIG_XIP_KERNEL
> + create_pgd_mapping(trampoline_pg_dir, XIP_VIRT_ADDR_START,
> + (uintptr_t)xip_pmd, PGDIR_SIZE, PAGE_TABLE);
> + for (va = XIP_VIRT_ADDR_START;
> + va < XIP_VIRT_ADDR_START + xiprom_sz;
> + va += PMD_SIZE) {
> + create_pmd_mapping(xip_pmd, va,
> + xiprom + (va - XIP_VIRT_ADDR_START),
> + PMD_SIZE, PAGE_KERNEL_EXEC);
> + }
> +
> + create_pgd_mapping(early_pg_dir, XIP_VIRT_ADDR_START,
> + (uintptr_t)xip_pmd, PGDIR_SIZE, PAGE_TABLE);
> +#endif
> +
> /*
> * Setup early PGD covering entire kernel which will allows
> * us to reach paging_init(). We map all memory banks later
> @@ -543,6 +637,9 @@ static void __init setup_vm_final(void)
> uintptr_t va, map_size;
> phys_addr_t pa, start, end;
> u64 i;
> +#ifdef CONFIG_XIP_KERNEL
> + uintptr_t xiprom_sz = (uintptr_t)(&_exiprom) - (uintptr_t)(&_xiprom);
> +#endif
>
> /**
> * MMU is enabled at this point. But page table setup is not complete yet.
> @@ -574,6 +671,25 @@ static void __init setup_vm_final(void)
> map_size, PAGE_KERNEL_EXEC);
> }
> }

Add new line here.

> +#ifdef CONFIG_XIP_KERNEL
> + for (va = XIP_VIRT_ADDR_START;
> + va < XIP_VIRT_ADDR_START + xiprom_sz;
> + va += PMD_SIZE)
> + create_pgd_mapping(swapper_pg_dir, va,
> + CONFIG_XIP_PHYS_ADDR + (va - XIP_VIRT_ADDR_START),
> + PMD_SIZE, PAGE_KERNEL_EXEC);
> +
> + /* if DT is in NOR, keep the early mapping */
> + if (dtb_early_pa >= CONFIG_XIP_PHYS_ADDR &&
> + dtb_early_pa <= CONFIG_XIP_PHYS_ADDR + SZ_16M) {
> + pa = dtb_early_pa & ~(PGDIR_SIZE - 1);
> + va = DTB_EARLY_BASE_VA;
> + create_pgd_mapping(swapper_pg_dir, va,
> + pa, PGDIR_SIZE, PAGE_KERNEL);
> + create_pgd_mapping(swapper_pg_dir, va + PGDIR_SIZE,
> + pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);

This is wasted of virtual address space for XIP kernel.

Also, DTB_EARLY_BASE_VA is an adhoc address falling in user-space
address range.

I would recommend XIP kernel to:
1. Allocate memory for DTB using memblock_phys_alloc()
2. The virtual addres of allocated memory can be found using __va()
3. Copy DTB to allocated memory
4. Set dtb_early_pa to new DTB location

> + }
> +#endif
>
> /* Clear fixmap PTE and PMD mappings */
> clear_fixmap(FIX_PTE);
> --
> 2.29.2
>

Regards,
Anup

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