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fix mm direcotry

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This commit is contained in:
Dongliang Mu
2018-03-15 00:25:26 -04:00
parent 1c8f44e45b
commit 1917026567
10 changed files with 23 additions and 23 deletions
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2
Concepts/linux-cpu-1.md
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@@ -91,7 +91,7 @@ early_param("percpu_alloc", percpu_alloc_setup);
enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;
```
如果内核命令行中没有设置 `percpu_alloc` 参数，就会使用 `embed` 分配器，将第一个 per-cpu 块嵌入进带 [memblock](http://0xax.gitbooks.io/linux-insides/content/mm/linux-mm-1.html) 的 bootmem。最后一个分配器和第一个块 `page` 分配器一样，只是将第一个块使用 `PAGE_SIZE` 页进行了映射。
如果内核命令行中没有设置 `percpu_alloc` 参数，就会使用 `embed` 分配器，将第一个 per-cpu 块嵌入进带 [memblock](http://0xax.gitbooks.io/linux-insides/content/MM/linux-mm-1.html) 的 bootmem。最后一个分配器和第一个块 `page` 分配器一样，只是将第一个块使用 `PAGE_SIZE` 页进行了映射。
如我上面所写，首先我们在 `setup_per_cpu_areas` 中对第一个块分配器检查，检查到第一个块分配器不是 page 分配器：

2
Initialization/linux-initialization-4.md
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@@ -349,7 +349,7 @@ Linux version 4.0.0-rc6+ (alex@localhost) (gcc version 4.9.1 (Ubuntu 4.9.1-16ubu
memblock_reserve(__pa_symbol(_text), (unsigned long)__bss_stop - (unsigned long)_text);
```
你可以阅读关于`memblock`的相关内容在[Linux kernel memory management Part 1.](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-1.html)，你应该还记得`memblock_reserve`函数的两个参数：
你可以阅读关于`memblock`的相关内容在[Linux kernel memory management Part 1.](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-1.html)，你应该还记得`memblock_reserve`函数的两个参数：
* base physical address of a memory block;
* size of a memory block.

4
Initialization/linux-initialization-6.md
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@@ -97,7 +97,7 @@ After this we can see call of the:
memblock_x86_reserve_range_setup_data();
```
function. This function is defined in the same [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) source code file and remaps memory for the `setup_data` and reserved memory block for the `setup_data` (more about `setup_data` you can read in the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-5.html) and about `ioremap` and `memblock` you can read in the [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)).
function. This function is defined in the same [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c) source code file and remaps memory for the `setup_data` and reserved memory block for the `setup_data` (more about `setup_data` you can read in the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-5.html) and about `ioremap` and `memblock` you can read in the [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html)).
In the next step we can see following conditional statement:
@@ -536,7 +536,7 @@ Links
* [Documentation/kernel-parameters.txt](https://github.com/torvalds/linux/blob/master/Documentation/kernel-parameters.txt)
* [APIC](http://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller)
* [CPU masks](http://0xax.gitbooks.io/linux-insides/content/Concepts/cpumask.html)
* [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)
* [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html)
* [PCI](http://en.wikipedia.org/wiki/Conventional_PCI)
* [e820](http://en.wikipedia.org/wiki/E820)
* [System Management BIOS](http://en.wikipedia.org/wiki/System_Management_BIOS)

4
Initialization/linux-initialization-7.md
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@@ -4,7 +4,7 @@ Kernel initialization. Part 7.
The End of the architecture-specific initialization, almost...
================================================================================
This is the seventh part of the Linux Kernel initialization process which covers insides of the `setup_arch` function from the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c#L861). As you can know from the previous [parts](http://0xax.gitbooks.io/linux-insides/content/Initialization/index.html), the `setup_arch` function does some architecture-specific (in our case it is [x86_64](http://en.wikipedia.org/wiki/X86-64)) initialization stuff like reserving memory for kernel code/data/bss, early scanning of the [Desktop Management Interface](http://en.wikipedia.org/wiki/Desktop_Management_Interface), early dump of the [PCI](http://en.wikipedia.org/wiki/PCI) device and many many more. If you have read the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/%20linux-initialization-6.html), you can remember that we've finished it at the `setup_real_mode` function. In the next step, as we set limit of the [memblock](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-1.html) to the all mapped pages, we can see the call of the `setup_log_buf` function from the [kernel/printk/printk.c](https://github.com/torvalds/linux/blob/master/kernel/printk/printk.c).
This is the seventh part of the Linux Kernel initialization process which covers insides of the `setup_arch` function from the [arch/x86/kernel/setup.c](https://github.com/torvalds/linux/blob/master/arch/x86/kernel/setup.c#L861). As you can know from the previous [parts](http://0xax.gitbooks.io/linux-insides/content/Initialization/index.html), the `setup_arch` function does some architecture-specific (in our case it is [x86_64](http://en.wikipedia.org/wiki/X86-64)) initialization stuff like reserving memory for kernel code/data/bss, early scanning of the [Desktop Management Interface](http://en.wikipedia.org/wiki/Desktop_Management_Interface), early dump of the [PCI](http://en.wikipedia.org/wiki/PCI) device and many many more. If you have read the previous [part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/%20linux-initialization-6.html), you can remember that we've finished it at the `setup_real_mode` function. In the next step, as we set limit of the [memblock](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-1.html) to the all mapped pages, we can see the call of the `setup_log_buf` function from the [kernel/printk/printk.c](https://github.com/torvalds/linux/blob/master/kernel/printk/printk.c).
The `setup_log_buf` function setups kernel cyclic buffer and its length depends on the `CONFIG_LOG_BUF_SHIFT` configuration option. As we can read from the documentation of the `CONFIG_LOG_BUF_SHIFT` it can be between `12` and `21`. In the insides, buffer defined as array of chars:
@@ -296,7 +296,7 @@ BUILD_BUG_ON((unsigned long)__fix_to_virt(VSYSCALL_PAGE) !=
(unsigned long)VSYSCALL_ADDR);
```
Now `vsyscall` area is in the `fix-mapped` area. That's all about `map_vsyscall`, if you do not know anything about fix-mapped addresses, you can read [Fix-Mapped Addresses and ioremap](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html). We will see more about `vsyscalls` in the `vsyscalls and vdso` part.
Now `vsyscall` area is in the `fix-mapped` area. That's all about `map_vsyscall`, if you do not know anything about fix-mapped addresses, you can read [Fix-Mapped Addresses and ioremap](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html). We will see more about `vsyscalls` in the `vsyscalls and vdso` part.
Getting the SMP configuration
--------------------------------------------------------------------------------

4
Initialization/linux-initialization-8.md
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@@ -230,7 +230,7 @@ pgtable_init();
vmalloc_init();
```
The first is `page_ext_init_flatmem` which depends on the `CONFIG_SPARSEMEM` kernel configuration option and initializes extended data per page handling. The `mem_init` releases all `bootmem`, the `kmem_cache_init` initializes kernel cache, the `percpu_init_late` - replaces `percpu` chunks with those allocated by [slub](http://en.wikipedia.org/wiki/SLUB_%28software%29), the `pgtable_init` - initializes the `page->ptl` kernel cache, the `vmalloc_init` - initializes `vmalloc`. Please, **NOTE** that we will not dive into details about all of these functions and concepts, but we will see all of they it in the [Linux kernel memory manager](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html) chapter.
The first is `page_ext_init_flatmem` which depends on the `CONFIG_SPARSEMEM` kernel configuration option and initializes extended data per page handling. The `mem_init` releases all `bootmem`, the `kmem_cache_init` initializes kernel cache, the `percpu_init_late` - replaces `percpu` chunks with those allocated by [slub](http://en.wikipedia.org/wiki/SLUB_%28software%29), the `pgtable_init` - initializes the `page->ptl` kernel cache, the `vmalloc_init` - initializes `vmalloc`. Please, **NOTE** that we will not dive into details about all of these functions and concepts, but we will see all of they it in the [Linux kernel memory manager](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html) chapter.
That's all. Now we can look on the `scheduler`.
@@ -465,7 +465,7 @@ Links
* [high-resolution kernel timer](https://www.kernel.org/doc/Documentation/timers/hrtimers.txt)
* [spinlock](http://en.wikipedia.org/wiki/Spinlock)
* [Run queue](http://en.wikipedia.org/wiki/Run_queue)
* [Linux kernem memory manager](http://0xax.gitbooks.io/linux-insides/content/mm/index.html)
* [Linux kernem memory manager](http://0xax.gitbooks.io/linux-insides/content/MM/index.html)
* [slub](http://en.wikipedia.org/wiki/SLUB_%28software%29)
* [virtual file system](http://en.wikipedia.org/wiki/Virtual_file_system)
* [Linux kernel hotplug documentation](https://www.kernel.org/doc/Documentation/cpu-hotplug.txt)

6
Initialization/linux-initialization-9.md
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@@ -83,7 +83,7 @@ void __init idr_init_cache(void)
}
```
Here we can see the call of the `kmem_cache_create`. We already called the `kmem_cache_init` in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c#L485). This function create generalized caches again using the `kmem_cache_alloc` (more about caches we will see in the [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html) chapter). In our case, as we are using `kmem_cache_t` which will be used by the [slab](http://en.wikipedia.org/wiki/Slab_allocation) allocator and `kmem_cache_create` creates it. As you can see we pass five parameters to the `kmem_cache_create`:
Here we can see the call of the `kmem_cache_create`. We already called the `kmem_cache_init` in the [init/main.c](https://github.com/torvalds/linux/blob/master/init/main.c#L485). This function create generalized caches again using the `kmem_cache_alloc` (more about caches we will see in the [Linux kernel memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html) chapter). In our case, as we are using `kmem_cache_t` which will be used by the [slab](http://en.wikipedia.org/wiki/Slab_allocation) allocator and `kmem_cache_create` creates it. As you can see we pass five parameters to the `kmem_cache_create`:
* name of the cache;
* size of the object to store in cache;
@@ -394,7 +394,7 @@ The next couple of functions are related with the [perf](https://perf.wiki.kerne
local_irq_enable();
```
which expands to the `sti` instruction and making post initialization of the [SLAB](http://en.wikipedia.org/wiki/Slab_allocation) with the call of the `kmem_cache_init_late` function (As I wrote above we will know about the `SLAB` in the [Linux memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html) chapter).
which expands to the `sti` instruction and making post initialization of the [SLAB](http://en.wikipedia.org/wiki/Slab_allocation) with the call of the `kmem_cache_init_late` function (As I wrote above we will know about the `SLAB` in the [Linux memory management](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html) chapter).
After the post initialization of the `SLAB`, next point is initialization of the console with the `console_init` function from the [drivers/tty/tty_io.c](https://github.com/torvalds/linux/blob/master/drivers/tty/tty_io.c).
@@ -424,7 +424,7 @@ Links
* [Documentation/memory-barriers.txt](https://www.kernel.org/doc/Documentation/memory-barriers.txt)
* [Runtime locking correctness validator](https://www.kernel.org/doc/Documentation/locking/lockdep-design.txt)
* [Per-CPU variables](http://xinqiu.gitbooks.io/linux-insides-cn/content/Concepts/per-cpu.html)
* [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/mm/index.html)
* [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/MM/index.html)
* [slab](http://en.wikipedia.org/wiki/Slab_allocation)
* [i2c](http://en.wikipedia.org/wiki/I%C2%B2C)
* [Previous part](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-8.html)

4
Interrupts/linux-interrupts-10.md
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@@ -257,7 +257,7 @@ if (!action)
return -ENOMEM;
```
欲知 `kzalloc` 详情，请查阅专门介绍 Linux 内核[内存管理](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)的章节。为 `irqaction` 分配空间后，我们即对这个结构体进行初始化，设置它的中断处理程序，中断标志，设备名称等等：
欲知 `kzalloc` 详情，请查阅专门介绍 Linux 内核[内存管理](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html)的章节。为 `irqaction` 分配空间后，我们即对这个结构体进行初始化，设置它的中断处理程序，中断标志，设备名称等等：
```C
action->handler = handler;
@@ -460,7 +460,7 @@ native_irq_return_iret:
* [initcall](http://kernelnewbies.org/Documents/InitcallMechanism)
* [uart](https://en.wikipedia.org/wiki/Universal_asynchronous_receiver/transmitter)
* [ISA](https://en.wikipedia.org/wiki/Industry_Standard_Architecture)
* [内存管理](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/index.html)
* [内存管理](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/index.html)
* [i2c](https://en.wikipedia.org/wiki/I%C2%B2C)
* [APIC](https://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller)
* [GNU 汇编器](https://en.wikipedia.org/wiki/GNU_Assembler)

10
Interrupts/linux-interrupts-4.md
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@@ -197,7 +197,7 @@ static int proc_root_readdir(struct file *file, struct dir_context *ctx)
}
```
Here we can see `proc_root_readdir` function which will be called when the Linux [VFS](https://en.wikipedia.org/wiki/Virtual_file_system) needs to read the `root` directory contents. If condition marked with `unlikely`, compiler can put `false` code right after branching. Now let's back to the our address check. Comparison between the given address and the `0x00007ffffffff000` will give us to know, was page fault in the kernel mode or user mode. After this check we know it. After this `__do_page_fault` routine will try to understand the problem that provoked page fault exception and then will pass address to the appropriate routine. It can be `kmemcheck` fault, spurious fault, [kprobes](https://www.kernel.org/doc/Documentation/kprobes.txt) fault and etc. Will not dive into implementation details of the page fault exception handler in this part, because we need to know many different concepts which are provided by the Linux kernel, but will see it in the chapter about the [memory management](http://0xax.gitbooks.io/linux-insides/content/mm/index.html) in the Linux kernel.
Here we can see `proc_root_readdir` function which will be called when the Linux [VFS](https://en.wikipedia.org/wiki/Virtual_file_system) needs to read the `root` directory contents. If condition marked with `unlikely`, compiler can put `false` code right after branching. Now let's back to the our address check. Comparison between the given address and the `0x00007ffffffff000` will give us to know, was page fault in the kernel mode or user mode. After this check we know it. After this `__do_page_fault` routine will try to understand the problem that provoked page fault exception and then will pass address to the appropriate routine. It can be `kmemcheck` fault, spurious fault, [kprobes](https://www.kernel.org/doc/Documentation/kprobes.txt) fault and etc. Will not dive into implementation details of the page fault exception handler in this part, because we need to know many different concepts which are provided by the Linux kernel, but will see it in the chapter about the [memory management](http://0xax.gitbooks.io/linux-insides/content/MM/index.html) in the Linux kernel.
Back to start_kernel
--------------------------------------------------------------------------------
@@ -214,7 +214,7 @@ There are many different function calls after the `early_trap_pf_init` in the `s
#endif
```
Note that it depends on the `CONFIG_EISA` kernel configuration parameter which represents `EISA` support. Here we use `early_ioremap` function to map `I/O` memory on the page tables. We use `readl` function to read first `4` bytes from the mapped region and if they are equal to `EISA` string we set `EISA_bus` to one. In the end we just unmap previously mapped region. More about `early_ioremap` you can read in the part which describes [Fix-Mapped Addresses and ioremap](http://0xax.gitbooks.io/linux-insides/content/mm/linux-mm-2.html).
Note that it depends on the `CONFIG_EISA` kernel configuration parameter which represents `EISA` support. Here we use `early_ioremap` function to map `I/O` memory on the page tables. We use `readl` function to read first `4` bytes from the mapped region and if they are equal to `EISA` string we set `EISA_bus` to one. In the end we just unmap previously mapped region. More about `early_ioremap` you can read in the part which describes [Fix-Mapped Addresses and ioremap](http://0xax.gitbooks.io/linux-insides/content/MM/linux-mm-2.html).
After this we start to fill the `Interrupt Descriptor Table` with the different interrupt gates. First of all we set `#DE` or `Divide Error` and `#NMI` or `Non-maskable Interrupt`:
@@ -329,7 +329,7 @@ __set_fixmap(FIX_RO_IDT, __pa_symbol(idt_table), PAGE_KERNEL_RO);
idt_descr.address = fix_to_virt(FIX_RO_IDT);
```
and write its address to the `idt_descr.address` (more about fix-mapped addresses you can read in the second part of the [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/mm/linux-mm-2.html) chapter). After this we can see the call of the `cpu_init` function that defined in the [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/cpu/common.c). This function makes initialization of the all `per-cpu` state. In the beginning of the `cpu_init` we do the following things: First of all we wait while current cpu is initialized and than we call the `cr4_init_shadow` function which stores shadow copy of the `cr4` control register for the current cpu and load CPU microcode if need with the following function calls:
and write its address to the `idt_descr.address` (more about fix-mapped addresses you can read in the second part of the [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/MM/linux-mm-2.html) chapter). After this we can see the call of the `cpu_init` function that defined in the [arch/x86/kernel/cpu/common.c](https://github.com/torvalds/linux/blob/16f73eb02d7e1765ccab3d2018e0bd98eb93d973/arch/x86/kernel/cpu/common.c). This function makes initialization of the all `per-cpu` state. In the beginning of the `cpu_init` we do the following things: First of all we wait while current cpu is initialized and than we call the `cr4_init_shadow` function which stores shadow copy of the `cr4` control register for the current cpu and load CPU microcode if need with the following function calls:
```C
wait_for_master_cpu(cpu);
@@ -448,8 +448,8 @@ Links
* [3DNow](https://en.wikipedia.org/?title=3DNow!)
* [CPU caches](https://en.wikipedia.org/wiki/CPU_cache)
* [VFS](https://en.wikipedia.org/wiki/Virtual_file_system)
* [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/mm/index.html)
* [Fix-Mapped Addresses and ioremap](http://0xax.gitbooks.io/linux-insides/content/mm/linux-mm-2.html)
* [Linux kernel memory management](http://0xax.gitbooks.io/linux-insides/content/MM/index.html)
* [Fix-Mapped Addresses and ioremap](http://0xax.gitbooks.io/linux-insides/content/MM/linux-mm-2.html)
* [Extended Industry Standard Architecture](https://en.wikipedia.org/wiki/Extended_Industry_Standard_Architecture)
* [INT isntruction](https://en.wikipedia.org/wiki/INT_%28x86_instruction%29)
* [INTO](http://x86.renejeschke.de/html/file_module_x86_id_142.html)

6
MM/linux-mm-3.md
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@@ -4,7 +4,7 @@ Linux内核内存管理 第三节
内核中 kmemcheck 介绍
--------------------------------------------------------------------------------
Linux内存管理[章节](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/)描述了Linux内核中[内存管理](https://en.wikipedia.org/wiki/Memory_management)；本小节是第三部分。 在本章[第二节](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html)中我们遇到了两个与内存管理相关的概念：
Linux内存管理[章节](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/)描述了Linux内核中[内存管理](https://en.wikipedia.org/wiki/Memory_management)；本小节是第三部分。 在本章[第二节](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html)中我们遇到了两个与内存管理相关的概念：
* `固定映射地址`;
* `输入输出重映射`.
@@ -62,7 +62,7 @@ $ sudo cat /proc/ioports
...
```
`ioports` 的输出列出了系统中物理设备所注册的各种类型的I/O端口。内核不能直接访问设备的输入/输出地址。在内核能够使用这些内存之前，必须将这些地址映射到虚拟地址空间，这就是`io remap`机制的主要目的。在前面[第二节](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html)中只介绍了早期的 `io remap` 。很快我们就要来看一看常规的 `io remap` 实现机制。但在此之前，我们需要学习一些其他的知识，例如不同类型的内存分配器等，不然的话我们很难理解该机制。
`ioports` 的输出列出了系统中物理设备所注册的各种类型的I/O端口。内核不能直接访问设备的输入/输出地址。在内核能够使用这些内存之前，必须将这些地址映射到虚拟地址空间，这就是`io remap`机制的主要目的。在前面[第二节](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html)中只介绍了早期的 `io remap` 。很快我们就要来看一看常规的 `io remap` 实现机制。但在此之前，我们需要学习一些其他的知识，例如不同类型的内存分配器等，不然的话我们很难理解该机制。
在进入Linux内核常规期的[内存管理](https://en.wikipedia.org/wiki/Memory_management)之前，我们要看一些特殊的内存机制，例如[调试](https://en.wikipedia.org/wiki/Debugging)，检查[内存泄漏](https://en.wikipedia.org/wiki/Memory_leak)，内存控制等等。学习这些内容有助于我们理解Linux内核的内存管理。
@@ -431,4 +431,4 @@ Links
* [flags register](https://en.wikipedia.org/wiki/FLAGS_register)
* [tasklet](https://xinqiu.gitbooks.io/linux-insides-cn/content/Interrupts/interrupts-9.html)
* [Paging](https://xinqiu.gitbooks.io/linux-insides-cn/content/Theory/Paging.html)
* [Previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html)
* [Previous part](https://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html)

4
SysCall/linux-syscall-3.md
View File

@@ -80,7 +80,7 @@ __vsyscall_page:
ret
```
回到 `map_vsyscall` 函数及 `__vsyscall_page` 的实现，在得到 `__vsyscall_page` 的物理地址之后，使用 `__set_fixmap` 为 `vsyscall` 内存页 检查设置 [fix-mapped](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html)地址的变量`vsyscall_mode`:
回到 `map_vsyscall` 函数及 `__vsyscall_page` 的实现，在得到 `__vsyscall_page` 的物理地址之后，使用 `__set_fixmap` 为 `vsyscall` 内存页 检查设置 [fix-mapped](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html)地址的变量`vsyscall_mode`:
```C
if (vsyscall_mode != NONE)
@@ -390,7 +390,7 @@ Links
* [virtual address](https://en.wikipedia.org/wiki/Virtual_address_space)
* [Segmentation](https://en.wikipedia.org/wiki/Memory_segmentation)
* [enum](https://en.wikipedia.org/wiki/Enumerated_type)
* [fix-mapped addresses](http://xinqiu.gitbooks.io/linux-insides-cn/content/mm/linux-mm-2.html)
* [fix-mapped addresses](http://xinqiu.gitbooks.io/linux-insides-cn/content/MM/linux-mm-2.html)
* [glibc](https://en.wikipedia.org/wiki/GNU_C_Library)
* [BUILD_BUG_ON](http://xinqiu.gitbooks.io/linux-insides-cn/content/Initialization/linux-initialization-1.html)
* [Processor register](https://en.wikipedia.org/wiki/Processor_register)