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Update linux-initialization-2.md

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Initialization/linux-initialization-2.md
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@ -442,9 +442,8 @@ And the `_AC` macro is defined in the [include/uapi/linux/const.h](https://elixi
#define _AC(X,Y) __AC(X,Y) #define _AC(X,Y) __AC(X,Y)
#endif #endif
``` ```
So, where `__PAGE_OFFSET` expands to `0xffff880000000000`. Where `__PAGE_OFFSET` expands to `0xffff880000000000`. But, why a virtual address can be translated to the physical address by simply subtracting `__PAGE_OFFSET`? The answer is in the [Documentation/x86/x86_64/mm.txt](https://elixir.bootlin.com/linux/v3.10-rc1/source/Documentation/x86/x86_64/mm.txt#L9) documentation:
Then, let's dive a little deeper. From Documentation/x86/x86_64/mm.txt:
``` ```
<previous description obsolete, deleted> <previous description obsolete, deleted>
@ -454,9 +453,9 @@ ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
... ...
``` ```
As you may see, the virtual address space `ffff880000000000-ffffc7ffffffffff` is direct mapping of all physical memory. When the kernel wants to access all physical memory, it uses direct mapping. As explained above, the virtual address space `ffff880000000000-ffffc7ffffffffff` is direct mapping of all physical memory. When the kernel wants to access all physical memory, it uses direct mapping.
We initialize `pmd` and pass it to the `__early_make_pgtable` function along with `address`. The `__early_make_pgtable` function is defined in the same file as the `early_make_pgtable` function as the following: Okay, let's get back to discussing `early_make_pgtable`. We initialize `pmd` and pass it to the `__early_make_pgtable` function along with `address`. The `__early_make_pgtable` function is defined in the same file as the `early_make_pgtable` function as the following:
```C ```C
int __init __early_make_pgtable(unsigned long address, pmdval_t pmd) int __init __early_make_pgtable(unsigned long address, pmdval_t pmd)