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Subject: Re: [PATCH v3 1/3] riscv: Move kernel mapping to vmalloc zone
From:   Alex Ghiti <alex@ghiti.fr>
To:     Zong Li <zong.li@sifive.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Anup Patel <Anup.Patel@wdc.com>,
        Atish Patra <Atish.Patra@wdc.com>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        linuxppc-dev@lists.ozlabs.org,
        linux-riscv <linux-riscv@lists.infradead.org>
References: <20200524085259.24784-1-alex@ghiti.fr>
 <20200524085259.24784-2-alex@ghiti.fr>
 <CANXhq0q_ba+zQrGUN0L+FQMPz6hWbYSQa2c8wLO3M-JTPWginA@mail.gmail.com>
 <6d6b09bc-32e4-4969-7020-12f9f02e557e@ghiti.fr>
 <CANXhq0qBOjFNvRB4QL-AoWzr5dU6Pz=tbf2qJMQxJjR99NHU3A@mail.gmail.com>
 <28e9d2ab-074c-90c2-73b5-a85d30f828cc@ghiti.fr>
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Date:   Thu, 28 May 2020 09:07:34 -0400
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Hi Zong,

Le 5/27/20 à 3:29 AM, Alex Ghiti a écrit :
> Le 5/27/20 à 2:05 AM, Zong Li a écrit :
>> On Wed, May 27, 2020 at 1:06 AM Alex Ghiti <alex@ghiti.fr> wrote:
>>> Hi Zong,
>>>
>>> Le 5/26/20 à 5:43 AM, Zong Li a écrit :
>>>> On Sun, May 24, 2020 at 4:54 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>>>>> This is a preparatory patch for relocatable kernel.
>>>>>
>>>>> The kernel used to be linked at PAGE_OFFSET address and used to be 
>>>>> loaded
>>>>> physically at the beginning of the main memory. Therefore, we 
>>>>> could use
>>>>> the linear mapping for the kernel mapping.
>>>>>
>>>>> But the relocated kernel base address will be different from 
>>>>> PAGE_OFFSET
>>>>> and since in the linear mapping, two different virtual addresses 
>>>>> cannot
>>>>> point to the same physical address, the kernel mapping needs to 
>>>>> lie outside
>>>>> the linear mapping.
>>>>>
>>>>> In addition, because modules and BPF must be close to the kernel 
>>>>> (inside
>>>>> +-2GB window), the kernel is placed at the end of the vmalloc zone 
>>>>> minus
>>>>> 2GB, which leaves room for modules and BPF. The kernel could not be
>>>>> placed at the beginning of the vmalloc zone since other vmalloc
>>>>> allocations from the kernel could get all the +-2GB window around the
>>>>> kernel which would prevent new modules and BPF programs to be loaded.
>>>>>
>>>>> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
>>>>> ---
>>>>>    arch/riscv/boot/loader.lds.S     |  3 +-
>>>>>    arch/riscv/include/asm/page.h    | 10 +++++-
>>>>>    arch/riscv/include/asm/pgtable.h | 37 +++++++++++++-------
>>>>>    arch/riscv/kernel/head.S         |  3 +-
>>>>>    arch/riscv/kernel/module.c       |  4 +--
>>>>>    arch/riscv/kernel/vmlinux.lds.S  |  3 +-
>>>>>    arch/riscv/mm/init.c             | 58 
>>>>> +++++++++++++++++++++++++-------
>>>>>    arch/riscv/mm/physaddr.c         |  2 +-
>>>>>    8 files changed, 87 insertions(+), 33 deletions(-)
>>>>>
>>>>> diff --git a/arch/riscv/boot/loader.lds.S 
>>>>> b/arch/riscv/boot/loader.lds.S
>>>>> index 47a5003c2e28..62d94696a19c 100644
>>>>> --- a/arch/riscv/boot/loader.lds.S
>>>>> +++ b/arch/riscv/boot/loader.lds.S
>>>>> @@ -1,13 +1,14 @@
>>>>>    /* SPDX-License-Identifier: GPL-2.0 */
>>>>>
>>>>>    #include <asm/page.h>
>>>>> +#include <asm/pgtable.h>
>>>>>
>>>>>    OUTPUT_ARCH(riscv)
>>>>>    ENTRY(_start)
>>>>>
>>>>>    SECTIONS
>>>>>    {
>>>>> -       . = PAGE_OFFSET;
>>>>> +       . = KERNEL_LINK_ADDR;
>>>>>
>>>>>           .payload : {
>>>>>                   *(.payload)
>>>>> diff --git a/arch/riscv/include/asm/page.h 
>>>>> b/arch/riscv/include/asm/page.h
>>>>> index 2d50f76efe48..48bb09b6a9b7 100644
>>>>> --- a/arch/riscv/include/asm/page.h
>>>>> +++ b/arch/riscv/include/asm/page.h
>>>>> @@ -90,18 +90,26 @@ typedef struct page *pgtable_t;
>>>>>
>>>>>    #ifdef CONFIG_MMU
>>>>>    extern unsigned long va_pa_offset;
>>>>> +extern unsigned long va_kernel_pa_offset;
>>>>>    extern unsigned long pfn_base;
>>>>>    #define ARCH_PFN_OFFSET                (pfn_base)
>>>>>    #else
>>>>>    #define va_pa_offset           0
>>>>> +#define va_kernel_pa_offset    0
>>>>>    #define ARCH_PFN_OFFSET                (PAGE_OFFSET >> PAGE_SHIFT)
>>>>>    #endif /* CONFIG_MMU */
>>>>>
>>>>>    extern unsigned long max_low_pfn;
>>>>>    extern unsigned long min_low_pfn;
>>>>> +extern unsigned long kernel_virt_addr;
>>>>>
>>>>>    #define __pa_to_va_nodebug(x)  ((void *)((unsigned long) (x) + 
>>>>> va_pa_offset))
>>>>> -#define __va_to_pa_nodebug(x)  ((unsigned long)(x) - va_pa_offset)
>>>>> +#define linear_mapping_va_to_pa(x)     ((unsigned long)(x) - 
>>>>> va_pa_offset)
>>>>> +#define kernel_mapping_va_to_pa(x)     \
>>>>> +       ((unsigned long)(x) - va_kernel_pa_offset)
>>>>> +#define __va_to_pa_nodebug(x)          \
>>>>> +       (((x) >= PAGE_OFFSET) ?         \
>>>>> +               linear_mapping_va_to_pa(x) : 
>>>>> kernel_mapping_va_to_pa(x))
>>>>>
>>>>>    #ifdef CONFIG_DEBUG_VIRTUAL
>>>>>    extern phys_addr_t __virt_to_phys(unsigned long x);
>>>>> diff --git a/arch/riscv/include/asm/pgtable.h 
>>>>> b/arch/riscv/include/asm/pgtable.h
>>>>> index 35b60035b6b0..25213cfaf680 100644
>>>>> --- a/arch/riscv/include/asm/pgtable.h
>>>>> +++ b/arch/riscv/include/asm/pgtable.h
>>>>> @@ -11,23 +11,29 @@
>>>>>
>>>>>    #include <asm/pgtable-bits.h>
>>>>>
>>>>> -#ifndef __ASSEMBLY__
>>>>> -
>>>>> -/* Page Upper Directory not used in RISC-V */
>>>>> -#include <asm-generic/pgtable-nopud.h>
>>>>> -#include <asm/page.h>
>>>>> -#include <asm/tlbflush.h>
>>>>> -#include <linux/mm_types.h>
>>>>> -
>>>>> -#ifdef CONFIG_MMU
>>>>> +#ifndef CONFIG_MMU
>>>>> +#define KERNEL_VIRT_ADDR       PAGE_OFFSET
>>>>> +#define KERNEL_LINK_ADDR       PAGE_OFFSET
>>>>> +#else
>>>>> +/*
>>>>> + * Leave 2GB for modules and BPF that must lie within a 2GB range 
>>>>> around
>>>>> + * the kernel.
>>>>> + */
>>>>> +#define KERNEL_VIRT_ADDR       (VMALLOC_END - SZ_2G + 1)
>>>>> +#define KERNEL_LINK_ADDR       KERNEL_VIRT_ADDR
>>>>>
>>>>>    #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)
>>>>> +#define BPF_JIT_REGION_START   (kernel_virt_addr)
>>>>> +#define BPF_JIT_REGION_END     (kernel_virt_addr + 
>>>>> BPF_JIT_REGION_SIZE)
>>>> It seems to have a potential risk here, the region of bpf is
>>>> overlapping with kernel mapping, so if kernel size is bigger than
>>>> 128MB, bpf region would be occupied and run out by kernel mapping.
>> Is there the risk as I mentioned?
>
>
> Sorry I forgot to answer this one: I was confident that 128MB was 
> large enough for kernel
> and BPF. But I see no reason to leave this risk so I'll change 
> kernel_virt_addr for _end so
> BPF will have its 128MB reserved.
>
> Thanks !
>
> Alex
>
>
>>
>>>>> +
>>>>> +#ifdef CONFIG_64BIT
>>>>> +#define VMALLOC_MODULE_START   BPF_JIT_REGION_END
>>>>> +#define VMALLOC_MODULE_END     VMALLOC_END
>>>>> +#endif
>>>>>
>>>> Although kernel_virt_addr is a fixed address now, I think it could be
>>>> changed for the purpose of relocatable or KASLR, so if
>>>> kernel_virt_addr is moved to far from VMALLOC_END than 2G, the region
>>>> of module would be too big.
>>>
>>> Yes you're right, that's wrong to allow modules to lie outside
>>> the 2G window, thanks for noticing.
>>>
>>>
>>>> In addition, the region of module could be
>>>> +-2G around the kernel, so we don't be limited in one direction as
>>>> before. It seems to me that the region of the module could be decided
>>>> at runtime, for example, VMALLOC_MODULE_START is "&_end - 2G" and
>>>> VMLLOC_MODULE_END is "&_start + 2G".
>>>
>>> I had tried that, but as we need to make sure BPF region is different
>>> from the module's
>>> that makes the macro definitions really cumbersome. I'll give a try
>>> again anyway. And
>>> I tried to use _end and _start here but it failed, I have to debug 
>>> this.


I gave more thought about that and it is actually not possible to use 
the 2GB
before and after the kernel: modules can call exported functions from 
each other,
so we need to make sure that the "distance" between 2 modules is at most 
2GB.
And I assume BPF comes with the same restrictions with respect to 
modules so the
kernel + BPF + modules must live in the same 2GB region.

I'll come with a v4 quickly,

Thanks,

Alex


>>>
>>>
>>>>    I'm not sure whether the size of
>>>> region of bpf has to be 128MB for some particular reason, if not,
>>>> maybe the region of bpf could be the same with module to avoid being
>>>> run out by module.
>>>
>>> On the contrary, BPF region must not be the same as module's since in
>>> that case,
>>> modules could take all the space and make BPF fail.
>> ok, I got it. Thanks for the explaining.
>>
>>
>>>
>>> Thanks for your review Zong,
>>>
>>>
>>> Alex
>>>
>>>
>>>>>    /*
>>>>>     * Roughly size the vmemmap space to be large enough to fit enough
>>>>> @@ -57,9 +63,16 @@
>>>>>    #define FIXADDR_SIZE     PGDIR_SIZE
>>>>>    #endif
>>>>>    #define FIXADDR_START    (FIXADDR_TOP - FIXADDR_SIZE)
>>>>> -
>>>>>    #endif
>>>>>
>>>>> +#ifndef __ASSEMBLY__
>>>>> +
>>>>> +/* Page Upper Directory not used in RISC-V */
>>>>> +#include <asm-generic/pgtable-nopud.h>
>>>>> +#include <asm/page.h>
>>>>> +#include <asm/tlbflush.h>
>>>>> +#include <linux/mm_types.h>
>>>>> +
>>>>>    #ifdef CONFIG_64BIT
>>>>>    #include <asm/pgtable-64.h>
>>>>>    #else
>>>>> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
>>>>> index 98a406474e7d..8f5bb7731327 100644
>>>>> --- a/arch/riscv/kernel/head.S
>>>>> +++ b/arch/riscv/kernel/head.S
>>>>> @@ -49,7 +49,8 @@ ENTRY(_start)
>>>>>    #ifdef CONFIG_MMU
>>>>>    relocate:
>>>>>           /* Relocate return address */
>>>>> -       li a1, PAGE_OFFSET
>>>>> +       la a1, kernel_virt_addr
>>>>> +       REG_L a1, 0(a1)
>>>>>           la a2, _start
>>>>>           sub a1, a1, a2
>>>>>           add ra, ra, a1
>>>>> diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
>>>>> index 8bbe5dbe1341..1a8fbe05accf 100644
>>>>> --- a/arch/riscv/kernel/module.c
>>>>> +++ b/arch/riscv/kernel/module.c
>>>>> @@ -392,12 +392,10 @@ int apply_relocate_add(Elf_Shdr *sechdrs, 
>>>>> const char *strtab,
>>>>>    }
>>>>>
>>>>>    #if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
>>>>> -#define VMALLOC_MODULE_START \
>>>>> -        max(PFN_ALIGN((unsigned long)&_end - SZ_2G), VMALLOC_START)
>>>>>    void *module_alloc(unsigned long size)
>>>>>    {
>>>>>           return __vmalloc_node_range(size, 1, VMALLOC_MODULE_START,
>>>>> -                                   VMALLOC_END, GFP_KERNEL,
>>>>> +                                   VMALLOC_MODULE_END, GFP_KERNEL,
>>>>>                                       PAGE_KERNEL_EXEC, 0, 
>>>>> NUMA_NO_NODE,
>>>>> __builtin_return_address(0));
>>>>>    }
>>>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S 
>>>>> b/arch/riscv/kernel/vmlinux.lds.S
>>>>> index 0339b6bbe11a..a9abde62909f 100644
>>>>> --- a/arch/riscv/kernel/vmlinux.lds.S
>>>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>>>>> @@ -4,7 +4,8 @@
>>>>>     * Copyright (C) 2017 SiFive
>>>>>     */
>>>>>
>>>>> -#define LOAD_OFFSET PAGE_OFFSET
>>>>> +#include <asm/pgtable.h>
>>>>> +#define LOAD_OFFSET KERNEL_LINK_ADDR
>>>>>    #include <asm/vmlinux.lds.h>
>>>>>    #include <asm/page.h>
>>>>>    #include <asm/cache.h>
>>>>> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
>>>>> index 27a334106708..17f108baec4f 100644
>>>>> --- a/arch/riscv/mm/init.c
>>>>> +++ b/arch/riscv/mm/init.c
>>>>> @@ -22,6 +22,9 @@
>>>>>
>>>>>    #include "../kernel/head.h"
>>>>>
>>>>> +unsigned long kernel_virt_addr = KERNEL_VIRT_ADDR;
>>>>> +EXPORT_SYMBOL(kernel_virt_addr);
>>>>> +
>>>>>    unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
>>>>> __page_aligned_bss;
>>>>>    EXPORT_SYMBOL(empty_zero_page);
>>>>> @@ -178,8 +181,12 @@ void __init setup_bootmem(void)
>>>>>    }
>>>>>
>>>>>    #ifdef CONFIG_MMU
>>>>> +/* Offset between linear mapping virtual address and kernel load 
>>>>> address */
>>>>>    unsigned long va_pa_offset;
>>>>>    EXPORT_SYMBOL(va_pa_offset);
>>>>> +/* Offset between kernel mapping virtual address and kernel load 
>>>>> address */
>>>>> +unsigned long va_kernel_pa_offset;
>>>>> +EXPORT_SYMBOL(va_kernel_pa_offset);
>>>>>    unsigned long pfn_base;
>>>>>    EXPORT_SYMBOL(pfn_base);
>>>>>
>>>>> @@ -271,7 +278,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>>>>>           if (mmu_enabled)
>>>>>                   return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>>>>
>>>>> -       pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
>>>>> +       pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
>>>>>           BUG_ON(pmd_num >= NUM_EARLY_PMDS);
>>>>>           return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
>>>>>    }
>>>>> @@ -372,14 +379,30 @@ static uintptr_t __init 
>>>>> best_map_size(phys_addr_t base, phys_addr_t size)
>>>>>    #error "setup_vm() is called from head.S before relocate so it 
>>>>> should not use absolute addressing."
>>>>>    #endif
>>>>>
>>>>> +static uintptr_t load_pa, load_sz;
>>>>> +
>>>>> +void create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
>>>>> +{
>>>>> +       uintptr_t va, end_va;
>>>>> +
>>>>> +       end_va = kernel_virt_addr + load_sz;
>>>>> +       for (va = kernel_virt_addr; va < end_va; va += map_size)
>>>>> +               create_pgd_mapping(pgdir, va,
>>>>> +                                  load_pa + (va - kernel_virt_addr),
>>>>> +                                  map_size, PAGE_KERNEL_EXEC);
>>>>> +}
>>>>> +
>>>>>    asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>>>>    {
>>>>>           uintptr_t va, end_va;
>>>>> -       uintptr_t load_pa = (uintptr_t)(&_start);
>>>>> -       uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
>>>>>           uintptr_t map_size = best_map_size(load_pa, 
>>>>> MAX_EARLY_MAPPING_SIZE);
>>>>>
>>>>> +       load_pa = (uintptr_t)(&_start);
>>>>> +       load_sz = (uintptr_t)(&_end) - load_pa;
>>>>> +
>>>>>           va_pa_offset = PAGE_OFFSET - load_pa;
>>>>> +       va_kernel_pa_offset = kernel_virt_addr - load_pa;
>>>>> +
>>>>>           pfn_base = PFN_DOWN(load_pa);
>>>>>
>>>>>           /*
>>>>> @@ -402,26 +425,22 @@ asmlinkage void __init setup_vm(uintptr_t 
>>>>> dtb_pa)
>>>>>           create_pmd_mapping(fixmap_pmd, FIXADDR_START,
>>>>>                              (uintptr_t)fixmap_pte, PMD_SIZE, 
>>>>> PAGE_TABLE);
>>>>>           /* Setup trampoline PGD and PMD */
>>>>> -       create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>>>> +       create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>>>                              (uintptr_t)trampoline_pmd, 
>>>>> PGDIR_SIZE, PAGE_TABLE);
>>>>> -       create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
>>>>> +       create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>>>>>                              load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>>>>>    #else
>>>>>           /* Setup trampoline PGD */
>>>>> -       create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
>>>>> +       create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
>>>>>                              load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
>>>>>    #endif
>>>>>
>>>>>           /*
>>>>> -        * Setup early PGD covering entire kernel which will allows
>>>>> +        * Setup early PGD covering entire kernel which will allow
>>>>>            * us to reach paging_init(). We map all memory banks later
>>>>>            * in setup_vm_final() below.
>>>>>            */
>>>>> -       end_va = PAGE_OFFSET + load_sz;
>>>>> -       for (va = PAGE_OFFSET; va < end_va; va += map_size)
>>>>> -               create_pgd_mapping(early_pg_dir, va,
>>>>> -                                  load_pa + (va - PAGE_OFFSET),
>>>>> -                                  map_size, PAGE_KERNEL_EXEC);
>>>>> +       create_kernel_page_table(early_pg_dir, map_size);
>>>>>
>>>>>           /* Create fixed mapping for early FDT parsing */
>>>>>           end_va = __fix_to_virt(FIX_FDT) + FIX_FDT_SIZE;
>>>>> @@ -441,6 +460,7 @@ static void __init setup_vm_final(void)
>>>>>           uintptr_t va, map_size;
>>>>>           phys_addr_t pa, start, end;
>>>>>           struct memblock_region *reg;
>>>>> +       static struct vm_struct vm_kernel = { 0 };
>>>>>
>>>>>           /* Set mmu_enabled flag */
>>>>>           mmu_enabled = true;
>>>>> @@ -467,10 +487,22 @@ static void __init setup_vm_final(void)
>>>>>                   for (pa = start; pa < end; pa += map_size) {
>>>>>                           va = (uintptr_t)__va(pa);
>>>>> create_pgd_mapping(swapper_pg_dir, va, pa,
>>>>> -                                          map_size, 
>>>>> PAGE_KERNEL_EXEC);
>>>>> +                                          map_size, PAGE_KERNEL);
>>>>>                   }
>>>>>           }
>>>>>
>>>>> +       /* Map the kernel */
>>>>> +       create_kernel_page_table(swapper_pg_dir, PMD_SIZE);
>>>>> +
>>>>> +       /* Reserve the vmalloc area occupied by the kernel */
>>>>> +       vm_kernel.addr = (void *)kernel_virt_addr;
>>>>> +       vm_kernel.phys_addr = load_pa;
>>>>> +       vm_kernel.size = (load_sz + PMD_SIZE) & ~(PMD_SIZE - 1);
>>>>> +       vm_kernel.flags = VM_MAP | VM_NO_GUARD;
>>>>> +       vm_kernel.caller = __builtin_return_address(0);
>>>>> +
>>>>> +       vm_area_add_early(&vm_kernel);
>>>>> +
>>>>>           /* Clear fixmap PTE and PMD mappings */
>>>>>           clear_fixmap(FIX_PTE);
>>>>>           clear_fixmap(FIX_PMD);
>>>>> diff --git a/arch/riscv/mm/physaddr.c b/arch/riscv/mm/physaddr.c
>>>>> index e8e4dcd39fed..35703d5ef5fd 100644
>>>>> --- a/arch/riscv/mm/physaddr.c
>>>>> +++ b/arch/riscv/mm/physaddr.c
>>>>> @@ -23,7 +23,7 @@ EXPORT_SYMBOL(__virt_to_phys);
>>>>>
>>>>>    phys_addr_t __phys_addr_symbol(unsigned long x)
>>>>>    {
>>>>> -       unsigned long kernel_start = (unsigned long)PAGE_OFFSET;
>>>>> +       unsigned long kernel_start = (unsigned long)kernel_virt_addr;
>>>>>           unsigned long kernel_end = (unsigned long)_end;
>>>>>
>>>>>           /*
>>>>> -- 
>>>>> 2.20.1
>>>>>