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From:   Alex Ghiti <alex@ghiti.fr>
Subject: Re: [PATCH v5] RISC-V: enable XIP
To:     Vitaly Wool <vitaly.wool@konsulko.com>
Cc:     linux-riscv <linux-riscv@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Bin Meng <bin.meng@windriver.com>,
        Anup Patel <anup@brainfault.org>,
        Alistair Francis <alistair.francis@wdc.com>,
        Palmer Dabbelt <palmerdabbelt@google.com>,
        Nicolas Pitre <nico@fluxnic.net>
References: <20210310092234.10501-1-vitaly.wool@konsulko.com>
 <82a05081-5662-c787-44e4-d480774ce31c@ghiti.fr>
 <CAM4kBBKU_qq=3An-nCbT-+AqsfAJhA=J8eocwNckVu8se001YA@mail.gmail.com>
Message-ID: <acb297b7-6efd-8eec-e50d-4ff2c3494e7d@ghiti.fr>
Date:   Mon, 22 Mar 2021 02:55:18 -0400
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Le 3/21/21 à 2:06 PM, Vitaly Wool a écrit :
> Hey Alex,
> 
> On Sun, Mar 21, 2021 at 4:11 PM Alex Ghiti <alex@ghiti.fr> wrote:
>>
>> Hi Vitaly,
>>
>> Le 3/10/21 à 4:22 AM, Vitaly Wool a écrit :
>>> 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
>>
>> There seems to be missing something here.
> 
> 
> Hmmm... strange indeed. I'll come up with a respin shortly and will
> double check.
>>
>>
>>> 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.
>>>
>>> Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
>>
>>
>> This fails to boot on current for-next with the following panic.
>> This is because dtb_early_va points to an address that is not mapped in
>> swapper_pg_dir: using __va(dtb_early_pa) instead works fine.
> 
> Is it with CONFIG_BUILTIN_DTB or without?

It is without CONFIG_BUILTIN_DTB enabled.

And I noticed I can't link a XIP_KERNEL either:

/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
section .data LMA [0000000000800000,00000000008cd77f] overlaps section 
.rodata LMA [00000000006f61c0,00000000008499a7]
/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
section .pci_fixup LMA [00000000008499a8,000000000084cfd7] overlaps 
section .data LMA [0000000000800000,00000000008cd77f]
/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
arch/riscv/mm/init.o: in function `.L138':
init.c:(.text+0x232): undefined reference to `__init_text_begin'
/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
arch/riscv/mm/init.o: in function `protect_kernel_text_data':
init.c:(.text+0x23a): undefined reference to `__init_data_begin'
/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
init.c:(.text+0x28c): undefined reference to `__init_text_begin'
/home/alex/wip/lpc/buildroot/build_rv64/host/bin/riscv64-buildroot-linux-gnu-ld: 
init.c:(.text+0x2a0): undefined reference to `__init_data_begin'
make[2]: *** [Makefile:1197: vmlinux] Error 1
make[1]: *** [package/pkg-generic.mk:250: 
/home/alex/wip/lpc/buildroot/build_rv64/build/linux-custom/.stamp_built] 
Error 2
make: *** [Makefile:23: _all] Error 2

The 2 missing symbols are not defined in vmlinux-xip.lds.S and are 
required for CONFIG_STRICT_KERNEL_RWX, I don't think both configs are 
exclusive ? I added them in linker script and that works.

But then I'm still blocked with the overlaps, any idea ?

> 
>>
>> And as this likely needs another version, I'm going to add my comments
>> below.
>>
>> [    0.000000] OF: fdt: Ignoring memory range 0x80000000 - 0x80200000
>> [    0.000000] Machine model: riscv-virtio,qemu
>> [    0.000000] earlycon: sbi0 at I/O port 0x0 (options '')
>> [    0.000000] printk: bootconsole [sbi0] enabled
>> [    0.000000] efi: UEFI not found.
>> [    0.000000] Unable to handle kernel paging request at virtual address
>> 0000000040000001
>> [    0.000000] Oops [#1]
>> [    0.000000] Modules linked in:
>> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.12.0-rc2 #155
>> [    0.000000] Hardware name: riscv-virtio,qemu (DT)
>> [    0.000000] epc : fdt_check_header+0x0/0x1fc
>> [    0.000000]  ra : early_init_dt_verify+0x16/0x6e
>> [    0.000000] epc : ffffffe0002b955e ra : ffffffe00082100c sp :
>> ffffffe001203f10
>> [    0.000000]  gp : ffffffe0012e40b8 tp : ffffffe00120bd80 t0 :
>> ffffffe23fdf7000
>> [    0.000000]  t1 : 0000000000000000 t2 : 0000000000000000 s0 :
>> ffffffe001203f30
>> [    0.000000]  s1 : 0000000040000000 a0 : 0000000040000000 a1 :
>> 00000002bfffffff
>> [    0.000000]  a2 : ffffffe23fdf6f00 a3 : 0000000000000001 a4 :
>> 0000000000000018
>> [    0.000000]  a5 : ffffffe000a0b5e8 a6 : ffffffe23fdf6ef0 a7 :
>> 0000000000000018
>> [    0.000000]  s2 : 0000000080000200 s3 : 0000000000000fff s4 :
>> ffffffe000a0a958
>> [    0.000000]  s5 : 0000000000000005 s6 : 0000000000000140 s7 :
>> ffffffe23fdf6ec0
>> [    0.000000]  s8 : 0000000081000200 s9 : 0000000080000200 s10:
>> ffffffe000a01000
>> [    0.000000]  s11: 0000000000000fff t3 : ffffffffbfff7000 t4 :
>> ffffffffffffffff
>> [    0.000000]  t5 : 0000000080e00000 t6 : 0000000080202000
>> [    0.000000] status: 0000000000000100 badaddr: 0000000040000001 cause:
>> 000000000000000d
>> [    0.000000] Call Trace:
>> [    0.000000] [<ffffffe0002b955e>] fdt_check_header+0x0/0x1fc
>> [    0.000000] [<ffffffe000802af2>] setup_arch+0x3a6/0x412
>> [    0.000000] [<ffffffe0008006ea>] start_kernel+0x7e/0x580
>> [    0.000000] random: get_random_bytes called from
>> print_oops_end_marker+0x22/0x44 with crng_init=0
>> [    0.000000] ---[ end trace 0000000000000000 ]---
>> [    0.000000] Kernel panic - not syncing: Fatal exception
>> [    0.000000] ---[ end Kernel panic - not syncing: Fatal exception ]---
>>
>>>
>>> ---
>>> Changes 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.
>>> Changes in v3:
>>> - rebased against latest for-next
>>> - XIP address fixup macro now takes an argument
>>> - SMP related fixes
>>> Changes in v4:
>>> - rebased against the current for-next
>>> - less #ifdef's in C/ASM code
>>> - dedicated XIP_FIXUP_OFFSET assembler macro in head.S
>>> - C-specific definitions moved into #ifndef __ASSEMBLY__
>>> - Fixed multi-core boot
>>> Changes in v5:
>>> - fixed build error for non-XIP kernels
>>>
>>>    arch/riscv/Kconfig                  |  44 +++++++++-
>>>    arch/riscv/Makefile                 |   8 +-
>>>    arch/riscv/boot/Makefile            |  13 +++
>>>    arch/riscv/include/asm/pgtable.h    |  65 ++++++++++++--
>>>    arch/riscv/kernel/cpu_ops_sbi.c     |  12 ++-
>>>    arch/riscv/kernel/head.S            |  59 ++++++++++++-
>>>    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                | 100 +++++++++++++++++++--
>>>    11 files changed, 432 insertions(+), 18 deletions(-)
>>>    create mode 100644 arch/riscv/kernel/vmlinux-xip.lds.S
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index 85d626b8ce5e..59fb945a900e 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -438,7 +438,7 @@ 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
>>> @@ -462,11 +462,51 @@ config STACKPROTECTOR_PER_TASK
>>>        def_bool y
>>>        depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_TLS
>>>
>>> +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.
>>
>> This is not XIP specific and this is something I considered to add in
>> order to map the linear mapping with hugepages, maybe simply rename this
>> without XIP_ prefix.
> 
> Sure, let's just go with PHYS_RAM_BASE. I was reluctant to add yet
> another constant at first but having to derive it in runtime led to
> overly complicated calculations which could not be compile time
> optimized, so here it came.
> 
>>> +
>>>    endmenu
>>>
>>>    config BUILTIN_DTB
>>> -     def_bool n
>>> +     bool
>>>        depends on OF
>>> +     default y if XIP_KERNEL
>>>
>>>    menu "Power management options"
>>>
>>> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>>> index 1368d943f1f3..8fcbec03974d 100644
>>> --- a/arch/riscv/Makefile
>>> +++ b/arch/riscv/Makefile
>>> @@ -82,7 +82,11 @@ 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
>>>
>>> @@ -95,12 +99,14 @@ PHONY += vdso_install
>>>    vdso_install:
>>>        $(Q)$(MAKE) $(build)=arch/riscv/kernel/vdso $@
>>>
>>> +ifneq ($(CONFIG_XIP_KERNEL),y)
>>>    ifeq ($(CONFIG_RISCV_M_MODE)$(CONFIG_SOC_CANAAN),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 ebf817c1bdf4..4c2e6902f2b8 100644
>>> --- a/arch/riscv/include/asm/pgtable.h
>>> +++ b/arch/riscv/include/asm/pgtable.h
>>> @@ -11,6 +11,33 @@
>>>
>>>    #include <asm/pgtable-bits.h>
>>>
>>> +#ifdef CONFIG_MMU
>>> +
>>> +#define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
>>> +
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +#define VMALLOC_SIZE     ((KERN_VIRT_SIZE >> 1) - SZ_16M)
>>> +#define VMALLOC_END      (PAGE_OFFSET - SZ_16M - 1)
>>> +
>>> +#define XIP_OFFSET           SZ_8M
>>> +#define XIP_MASK             (SZ_8M - 1)
>>> +#define XIP_VIRT_ADDR(physaddr)      \
>>> +     (PAGE_OFFSET - XIP_OFFSET + ((physaddr) & XIP_MASK))
>>> +
>>> +#else
>>> +
>>> +#define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
>>> +#define VMALLOC_END      (PAGE_OFFSET - 1)
>>> +
>>> +#endif /* CONFIG_XIP_KERNEL */
>>> +
>>> +#else
>>> +
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +#define XIP_VIRT_ADDR(physaddr) (physaddr)
>>> +#endif /* CONFIG_XIP_KERNEL */
>>> +#endif /* CONFIG_MMU */
>>> +
>>>    #ifndef __ASSEMBLY__
>>>
>>>    /* Page Upper Directory not used in RISC-V */
>>> @@ -21,9 +48,25 @@
>>>
>>>    #ifdef CONFIG_MMU
>>>
>>> -#define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
>>> -#define VMALLOC_END      (PAGE_OFFSET - 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.
>>
>> It seems the comment should be the other way around: "this macro
>> replaces the *virtual* address...etc".

Isn't there an issue with the comment here ?

>>
>>> + */
>>> +#define XIP_PHYS_ADDR(va)     \
>>> +     ((uintptr_t)(va) - PAGE_OFFSET + XIP_OFFSET + CONFIG_XIP_PHYS_ADDR)
>>> +
>>> +#define XIP_VIRT_ADDR_START  XIP_VIRT_ADDR(CONFIG_XIP_PHYS_ADDR)
>>> +#define __PHRAM_BASE         CONFIG_XIP_PHYS_RAM_BASE
>>
>> I don't think that it is necessary to define this intermediate
>> __PHRAM_BASE.
> 
> That was for the sake of keeping shorter lines. :)
> 
>>> +
>>> +#define XIP_FIXUP(addr)              \
>>> +     (((uintptr_t)(addr) >= CONFIG_XIP_PHYS_ADDR && \
>>> +       (uintptr_t)(addr) <= CONFIG_XIP_PHYS_ADDR + SZ_16M) ? \
>>
>> That should be < CONFIG_XIP_PHYS_ADDR + SZ_16M, not <=.
> 
> Thanks, will fix.
> 
>>> +     (uintptr_t)(addr) - CONFIG_XIP_PHYS_ADDR + __PHRAM_BASE - XIP_OFFSET : \
>>> +     (uintptr_t)(addr))
>>
>> There are possible side-effects in this macro definition, consider using
>> a temporary variable for addr.
> 
> This is an internal definition so I didn't care much but FWIW it's
> better to change it as you suggest, thanks.
> 
>>> +#else
>>> +#define XIP_FIXUP(addr)              (addr)
>>> +#endif /* CONFIG_XIP_KERNEL */
>>>
>>>    #define BPF_JIT_REGION_SIZE (SZ_128M)
>>>    #define BPF_JIT_REGION_START        (PAGE_OFFSET - BPF_JIT_REGION_SIZE)
>>> @@ -484,8 +527,20 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
>>>
>>>    #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)
>>
>> CONFIG_XIP_KERNEL already depends on CONFIG_MMU. And maybe we could
>> handle XIP_KERNEL and !XIP_KERNEL in XIP_FIXUP to avoid those ifdefs ?
> 
> This is a temporary dependence, we are working on the non-MMU case too
> so I would not like to go that path.
> 
>>> +
>>> +#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);
>>>    void misc_mem_init(void);
>>> diff --git a/arch/riscv/kernel/cpu_ops_sbi.c b/arch/riscv/kernel/cpu_ops_sbi.c
>>> index 685fae72b7f5..7d368bc656ff 100644
>>> --- a/arch/riscv/kernel/cpu_ops_sbi.c
>>> +++ b/arch/riscv/kernel/cpu_ops_sbi.c
>>> @@ -53,10 +53,20 @@ static int sbi_hsm_hart_get_status(unsigned long hartid)
>>>    }
>>>    #endif
>>>
>>> +static inline unsigned long get_secondary_start_phys(void)
>>> +{
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +     return XIP_PHYS_ADDR(secondary_start_sbi);
>>> +#else
>>> +     return __pa_symbol(secondary_start_sbi);
>>> +#endif
>>> +}
>>> +
>>> +
>>
>> There are 2 newlines here.
>>
>>>    static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle)
>>>    {
>>>        int rc;
>>> -     unsigned long boot_addr = __pa_symbol(secondary_start_sbi);
>>> +     unsigned long boot_addr = get_secondary_start_phys();
>>>        int hartid = cpuid_to_hartid_map(cpuid);
>>>
>>>        cpu_update_secondary_bootdata(cpuid, tidle);
>>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>>> index f5a9bad86e58..17ecf6095209 100644
>>> --- a/arch/riscv/kernel/head.S
>>> +++ b/arch/riscv/kernel/head.S
>>> @@ -9,11 +9,33 @@
>>>    #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
>>
>> Use REG_L here.
> 
> Will do, thanks.
> 
>>> +             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
>>> +#else
>>> +.macro XIP_FIXUP_OFFSET reg
>>> +.endm
>>> +#endif /* CONFIG_XIP_KERNEL */
>>> +
>>>    __HEAD
>>>    ENTRY(_start)
>>>        /*
>>> @@ -69,7 +91,11 @@ 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
>>> @@ -91,6 +117,7 @@ relocate:
>>>         * to ensure the new translations are in use.
>>>         */
>>>        la a0, trampoline_pg_dir
>>> +     XIP_FIXUP_OFFSET a0
>>
>>
>> For all those pairs of la aX...; XIP_FIXUP_OFFSET aX...; maybe introduce
>> a macro that does both ?
> 
> I can do that but wouldn't it obscure the operations too much?
> 

IMHO, this would avoid to break XIP_KERNEL if we don't have to worry 
about those fixup, because as this adds a new kernel, I'm a bit worried 
we break it over time easily.

>>>        srl a0, a0, PAGE_SHIFT
>>>        or a0, a0, a1
>>>        sfence.vma
>>> @@ -144,7 +171,9 @@ secondary_start_sbi:
>>>
>>>        slli a3, a0, LGREG
>>>        la a4, __cpu_up_stack_pointer
>>> +     XIP_FIXUP_OFFSET a4
>>>        la a5, __cpu_up_task_pointer
>>> +     XIP_FIXUP_OFFSET a5
>>>        add a4, a3, a4
>>>        add a5, a3, a5
>>>        REG_L sp, (a4)
>>> @@ -156,6 +185,7 @@ secondary_start_common:
>>>    #ifdef CONFIG_MMU
>>>        /* Enable virtual memory and relocate to virtual address */
>>>        la a0, swapper_pg_dir
>>> +     XIP_FIXUP_OFFSET a0
>>>        call relocate
>>>    #endif
>>>        call setup_trap_vector
>>> @@ -236,12 +266,33 @@ pmp_done:
>>>    .Lgood_cores:
>>>    #endif
>>>
>>> +#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
>>> +     lw t1, (a3)
>>> +     amoswap.w t0, t1, (a2)
>>> +     /* first time here if hart_lottery in RAM is not set */
>>> +     beq t0, t1, .Lsecondary_start
>>> +
>>> +     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
>>> @@ -251,15 +302,18 @@ 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
>>> +     XIP_FIXUP_OFFSET a2
>>>        REG_S a0, (a2)
>>>
>>>        /* Initialize page tables and relocate to virtual addresses */
>>>        la sp, init_thread_union + THREAD_SIZE
>>> +     XIP_FIXUP_OFFSET sp
>>>    #ifdef CONFIG_BUILTIN_DTB
>>>        la a0, __dtb_start
>>>    #else
>>> @@ -268,6 +322,7 @@ clear_bss_done:
>>>        call setup_vm
>>>    #ifdef CONFIG_MMU
>>>        la a0, early_pg_dir
>>> +     XIP_FIXUP_OFFSET a0
>>>        call relocate
>>>    #endif /* CONFIG_MMU */
>>>
>>> @@ -292,7 +347,9 @@ clear_bss_done:
>>>
>>>        slli a3, a0, LGREG
>>>        la a1, __cpu_up_stack_pointer
>>> +     XIP_FIXUP_OFFSET a1
>>>        la a2, __cpu_up_task_pointer
>>> +     XIP_FIXUP_OFFSET a2
>>>        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 e85bacff1b50..29956c41a9cc 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(0xC001BEEF)
>>> +#endif
>>> +;
>>>    unsigned long boot_cpu_hartid;
>>>    static DEFINE_PER_CPU(struct cpu, cpu_devices);
>>>
>>> @@ -254,7 +258,7 @@ 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))
>>>                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
>>> +}
>>> 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 067583ab1bd7..b5ac455cb159 100644
>>> --- a/arch/riscv/mm/init.c
>>> +++ b/arch/riscv/mm/init.c
>>> @@ -31,8 +31,8 @@ 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);
>>> @@ -88,6 +88,10 @@ 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) { }
>>> @@ -113,6 +117,10 @@ void __init setup_bootmem(void)
>>>        phys_addr_t dram_end = memblock_end_of_DRAM();
>>>        phys_addr_t max_mapped_addr = __pa(~(ulong)0);
>>>
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +     vmlinux_start = __pa_symbol(&_sdata);
>>> +#endif
>>
>> Nit: I would use IS_ENABLED(CONFIG_XIP_KERNEL) to avoid double
>> assignment in case CONFIG_XIP_KERNEL is set.
>>
>>> +
>>>        /* The maximal physical memory size is -PAGE_OFFSET. */
>>>        memblock_enforce_memory_limit(-PAGE_OFFSET);
>>>
>>> @@ -148,11 +156,27 @@ void __init setup_bootmem(void)
>>>        memblock_allow_resize();
>>>    }
>>>
>>> +#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);
>>>
>>> @@ -162,6 +186,12 @@ pte_t fixmap_pte[PTRS_PER_PTE] __page_aligned_bss;
>>>
>>>    pgd_t early_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
>>>
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +#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))
>>> +#endif /* CONFIG_XIP_KERNEL */
>>> +
>>>    void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
>>>    {
>>>        unsigned long addr = __fix_to_virt(idx);
>>> @@ -237,6 +267,15 @@ pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
>>>    pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>>>    pmd_t early_dtb_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
>>>
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +pmd_t xip_pmd[PTRS_PER_PMD] __page_aligned_bss;
>>> +
>>> +#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))
>>> +#endif /* CONFIG_XIP_KERNEL */
>>> +
>>>    static pmd_t *__init get_pmd_virt_early(phys_addr_t pa)
>>>    {
>>>        /* Before MMU is enabled */
>>> @@ -353,6 +392,19 @@ 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.
>>>     *
>>> @@ -373,7 +425,8 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
>>>
>>>    asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>    {
>>> -     uintptr_t va, pa, end_va;
>>> +     uintptr_t va, end_va;
>>> +     uintptr_t __maybe_unused pa;
>>>        uintptr_t load_pa = (uintptr_t)(&_start);
>>>        uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>>>        uintptr_t map_size;
>>> @@ -381,6 +434,13 @@ 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);
>>> +
>>> +     load_pa = (uintptr_t)CONFIG_XIP_PHYS_RAM_BASE;
>>> +     load_sz = (uintptr_t)(&_end) - (uintptr_t)(&_sdata);
>>> +#endif
>>>        va_pa_offset = PAGE_OFFSET - load_pa;
>>>        pfn_base = PFN_DOWN(load_pa);
>>>
>>> @@ -419,6 +479,21 @@ 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
>>> @@ -443,7 +518,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>                           pa + PMD_SIZE, PMD_SIZE, PAGE_KERNEL);
>>>        dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PMD_SIZE - 1));
>>>    #else /* CONFIG_BUILTIN_DTB */
>>> -     dtb_early_va = __va(dtb_pa);
>>> +     dtb_early_va = __va(XIP_FIXUP(dtb_pa));
>>>    #endif /* CONFIG_BUILTIN_DTB */
>>>    #else
>>>    #ifndef CONFIG_BUILTIN_DTB
>>> @@ -455,7 +530,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>                           pa + PGDIR_SIZE, PGDIR_SIZE, PAGE_KERNEL);
>>>        dtb_early_va = (void *)DTB_EARLY_BASE_VA + (dtb_pa & (PGDIR_SIZE - 1));
>>>    #else /* CONFIG_BUILTIN_DTB */
>>> -     dtb_early_va = __va(dtb_pa);
>>> +     dtb_early_va = __va(XIP_FIXUP(dtb_pa));
>>>    #endif /* CONFIG_BUILTIN_DTB */
>>>    #endif
>>>        dtb_early_pa = dtb_pa;
>>> @@ -496,6 +571,9 @@ 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.
>>> @@ -527,6 +605,16 @@ static void __init setup_vm_final(void)
>>>                                           map_size, PAGE_KERNEL_EXEC);
>>>                }
>>>        }
>>> +#ifdef CONFIG_XIP_KERNEL
>>> +     map_size = best_map_size(CONFIG_XIP_PHYS_ADDR, xiprom_sz);
>>> +     for (va = XIP_VIRT_ADDR_START;
>>> +          va < XIP_VIRT_ADDR_START + xiprom_sz;
>>> +          va += map_size)
>>> +             create_pgd_mapping(swapper_pg_dir, va,
>>> +                                CONFIG_XIP_PHYS_ADDR + (va - XIP_VIRT_ADDR_START),
>>> +                                map_size, PAGE_KERNEL_EXEC);
>>> +
>>> +#endif
>>>
>>>        /* Clear fixmap PTE and PMD mappings */
>>>        clear_fixmap(FIX_PTE);
>>>
>>
>> And I'm not sure I understand which variables are required to be fixup,
>> can you explain it a bit more please ?
> 
> On a high level, all the RW sections are copied to RAM but while the
> MMU is not enabled, we are dealing with the addresses in the NOR flash
> all the way. To read and modify the RAM versions of variables we do
> this XIP_FIXUP thing.

Ok thanks, we'll need to be extra careful when touching the pre-mmu zone 
then.

> 
> Please come back if this explanation is not clear enough.
> 
>> And finally, how can we try XIP_KERNEL on qemu ?
> 
> It works with Polarfire Icicle emulation. I'm using the folllowing
> command line for testing it:
> qemu-system-riscv64 -M microchip-icicle-kit -bios
> work/hart-software-services/hss.bin -smp 5 -drive
> if=sd,format=raw,file=sd1.img -nic user,model=cadence_gem -display
> none -serial null -chardev
> socket,id=serial1,path=/tmp/serial1.sock,server -serial
> chardev:serial1 -device loader,addr=0x21000000,file=xipImage -D
> qemu.log -monitor stdio
> 

Thanks for the qemu command line !

> Thanks a lot for the review,
> 
> Best regards,
>     Vitaly

Thanks,

Alex

> 
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