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分类: LINUX

2009-12-11 20:39:10

Written by leeming

这一讲是主要讲setup_arch中那个没有解释的函数解释完毕,完成setup_arch的函数,好让我们的start_kernel继续下去。

/*

 * paging_init() sets up the page tables, initialises the zone memory

 * maps, and sets up the zero page, bad page and bad page tables.

 *这部分的主要工作建立页表,初始化内存。

*/

void __init paging_init(struct meminfo *mi, struct machine_desc *mdesc)

{

       void *zero_page;

//这个函数主要是用来建立各种类型的页表选项(比如内存是MEMORY类型,设备室DEVICE,中断向量表是HIGH_VECTORS)

       build_mem_type_table();

{

       struct cachepolicy *cp;

       //获取cp15处理器的c1寄存器位

       unsigned int cr = get_cr();

       unsigned int user_pgprot, kern_pgprot;

       //获取处理器架构版本

       int cpu_arch = cpu_architecture();

       int i;

 

       //根据处理器版本号调整cache政策,不是写缓冲区的政策

#if defined(CONFIG_CPU_DCACHE_DISABLE)

       if (cachepolicy > CPOLICY_BUFFERED)

              cachepolicy = CPOLICY_BUFFERED;

#elif defined(CONFIG_CPU_DCACHE_WRITETHROUGH)

       if (cachepolicy > CPOLICY_WRITETHROUGH)

              cachepolicy = CPOLICY_WRITETHROUGH;

#endif

       if (cpu_arch < CPU_ARCH_ARMv5) {

              if (cachepolicy >= CPOLICY_WRITEALLOC)

                     cachepolicy = CPOLICY_WRITEBACK;

              ecc_mask = 0;//因为v5前的处理器的一级描述符没有定义第9位作为保护标志位

       }

 

       if (cpu_arch <= CPU_ARCH_ARMv5TEJ) {

              //mem_types是一个全局数组arch/arm/mm-armv.c,里面有所有类型

              for (i = 0; i < ARRAY_SIZE(mem_types); i++) {

                     //prot_l1 prot_sect都是一级描述符的意思

                     //将一级描述符的第4位置1

                     if (mem_types[i].prot_l1)

                            mem_types[i].prot_l1 |= PMD_BIT4;

                     if (mem_types[i].prot_sect)

                            mem_types[i].prot_sect |= PMD_BIT4;

              }

       }

 

       //我们的cachepolicy3,因此相应的配置如下

       //     .policy          = "writeback",

       //     .cr_mask       = 0,

       //     .pmd             = PMD_SECT_WB,

       //     .pte        = PTE_BUFFERABLE|PTE_CACHEABLE,

       cp = &cache_policies[cachepolicy];

       //kern_pgprot user_pgprot是内核和用户空间的二级页表描述符

       kern_pgprot = user_pgprot = cp->pte;

 

       //以下删除了非v4t架构的高版本代码

 

       for (i = 0; i < 16; i++) {

              //这里依次获取16个默认的保护类型的值

              unsigned long v = pgprot_val(protection_map[i]);

              //(L_PTE_BUFFERABLE|L_PTE_CACHEABLE)这是linux pte的定义

              //内核中有linuxhardware两种定义方式,为了更好的兼容性

              //这里两者间是匹配的,这里将值再加上我们的设置就是

              //最新的16个值,将它写回更新

              v = (v & ~(L_PTE_BUFFERABLE|L_PTE_CACHEABLE)) | user_pgprot;

              protection_map[i] = __pgprot(v);

       }

 

       mem_types[MT_LOW_VECTORS].prot_pte |= kern_pgprot;

       mem_types[MT_HIGH_VECTORS].prot_pte |= kern_pgprot;

       mem_types[MT_MINICLEAN].prot_sect &= ~PMD_SECT_TEX(1);

 

       pgprot_kernel = __pgprot(L_PTE_PRESENT | L_PTE_YOUNG |

                             L_PTE_DIRTY | L_PTE_WRITE |

                             L_PTE_EXEC | kern_pgprot);

 

       mem_types[MT_LOW_VECTORS].prot_l1 |= ecc_mask;

       mem_types[MT_HIGH_VECTORS].prot_l1 |= ecc_mask;

       mem_types[MT_MEMORY].prot_sect |= ecc_mask | cp->pmd;

       mem_types[MT_ROM].prot_sect |= cp->pmd;

 

       switch (cp->pmd) {

       case PMD_SECT_WT:

              mem_types[MT_CACHECLEAN].prot_sect |= PMD_SECT_WT;

              break;

       case PMD_SECT_WB:

       case PMD_SECT_WBWA:

              mem_types[MT_CACHECLEAN].prot_sect |= PMD_SECT_WB;

              break;

       }

       //以上所有的操作都是为了给mem_types这个结构体中的各种类型中的页表参数添加上我们的要求,主要是一级页表,二级页表,ap(访问权限控制);至于domain是利用系统初始化时的值,不用我们再进行干预。

//系统的domain类型一共有四种,kernel——0user——1io——2

       printk("Memory policy: ECC %sabled, Data cache %s\n",

              ecc_mask ? "en" : "dis", cp->policy);

}

       bootmem_init(mi);

{

              unsigned long addr, memend_pfn = 0;

       int node, initrd_node, i;

 

       /*

        * Invalidate the node number for empty or invalid memory banks

        */

       for (i = 0; i < mi->nr_banks; i++)

              if (mi->bank[i].size == 0 || mi->bank[i].node >= MAX_NUMNODES)

                     mi->bank[i].node = -1;

 

       //将在4020.c fixup函数中定义的内存信息添加到meminfo结构体中

       memcpy(&meminfo, mi, sizeof(meminfo));

 

      

 //MODULE_START0xc0000000-16M; 2M为单位,清除内核空间一下的用户空间

       for (addr = 0; addr < MODULE_START; addr += PGDIR_SIZE)

//内核在进入保护模式前, 还没有启用分页功能, 在这之前内核要先建立一个临时内核页表,因为在进入保护模式后, 内核继续初始化直到建

//立完整的内存映射机制之前, 仍然需要用到页表来映射相应的内存地址。 临时页表的初始化是在arch/i386/kernel/head.S中进行的:

//swapper_pg_dir是临时页全局目录表, 它是在内核编译过程中静态初始化的.

//pg0是第一个页表开始的地方, 它也是内核编译过程中静态初始化的.

//pmd_off_k是获取虚拟地址为addr的页表项地址

//pmd_clear是将()中的页表项地址中的数据清0

       pmd_clear(pmd_off_k(addr));

      

#ifdef CONFIG_XIP_KERNEL

       /* The XIP kernel is mapped in the module area -- skip over it */

       addr = ((unsigned long)&_etext + PGDIR_SIZE - 1) & PGDIR_MASK;

#endif

 

       //防止xip之后会有变化,检查,做一次用户空间的清除

       for ( ; addr < PAGE_OFFSET; addr += PGDIR_SIZE)

              pmd_clear(pmd_off_k(addr));

 

       /*

        * Clear out all the kernel space mappings, except for the first

        * memory bank, up to the end of the vmalloc region.

        */

        //清除内核空间,但是不清楚内存所在区域,也就是

        //0xc2000000-0xd0000000的空间

       for (addr = __phys_to_virt(mi->bank[0].start + mi->bank[0].size);

            addr < VMALLOC_END; addr += PGDIR_SIZE)

              pmd_clear(pmd_off_k(addr));

 

       /*

        * Locate which node contains the ramdisk image, if any.

        */

        //返回如果有initrd所在的内存节点

       initrd_node = check_initrd(mi);

 

       /*

        * Run through each node initialising the bootmem allocator.

        */

       for_each_node(node) {

              unsigned long end_pfn;

 

              //为内存建立一级页表(多的话还有二级页表)

              end_pfn = bootmem_init_node(node, initrd_node, mi);

 

              /*

               * Remember the highest memory PFN.

               */

              if (end_pfn > memend_pfn)

                     memend_pfn = end_pfn;

       }

 

       high_memory = __va(memend_pfn << PAGE_SHIFT);

 

       /*

        * This doesn't seem to be used by the Linux memory manager any

        * more, but is used by ll_rw_block.  If we can get rid of it, we

        * also get rid of some of the stuff above as well.

        *

        * Note: max_low_pfn and max_pfn reflect the number of _pages_ in

        * the system, not the maximum PFN.

        */

       max_pfn = max_low_pfn = memend_pfn - PHYS_PFN_OFFSET;

}

       devicemaps_init(mdesc);

{

       struct map_desc map;

       unsigned long addr;

       void *vectors;

 

       /*

        * Allocate the vector page early.

        */

        //为中断向量表申请一页的空间,申请的位置

        //就是之前在内存中建立的页表的物理地址

       vectors = alloc_bootmem_low_pages(PAGE_SIZE);

       BUG_ON(!vectors);

 

       for (addr = VMALLOC_END; addr; addr += PGDIR_SIZE)

       //pmd_off_k是获取虚拟地址为addr的页表项地址

       //pmd_clear是将()中的页表项地址中的数据清0

              pmd_clear(pmd_off_k(addr));

 

       /*

        * Map the kernel if it is XIP.

        * It is always first in the modulearea.

        */

#ifdef CONFIG_XIP_KERNEL

       map.pfn = __phys_to_pfn(CONFIG_XIP_PHYS_ADDR & PGDIR_MASK);

       map.virtual = MODULE_START;

       map.length = ((unsigned long)&_etext - map.virtual + ~PGDIR_MASK) & PGDIR_MASK;

       map.type = MT_ROM;

       create_mapping(&map);

#endif

 

       /*

        * Map the cache flushing regions.

        */

#ifdef FLUSH_BASE

       map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS);

       map.virtual = FLUSH_BASE;

       map.length = PGDIR_SIZE;

       map.type = MT_CACHECLEAN;

       create_mapping(&map);

#endif

#ifdef FLUSH_BASE_MINICACHE

       map.pfn = __phys_to_pfn(FLUSH_BASE_PHYS + PGDIR_SIZE);

       map.virtual = FLUSH_BASE_MINICACHE;

       map.length = PGDIR_SIZE;

       map.type = MT_MINICLEAN;

       create_mapping(&map);

#endif

 

       /*

        * Create a mapping for the machine vectors at the high-vectors

        * location (0xffff0000).  If we aren't using high-vectors, also

        * create a mapping at the low-vectors virtual address.

        */

        //为中断向量表建立页映射,相应的选项配置在

        //build_mem_type_table()中已经设置好了

       map.pfn = __phys_to_pfn(virt_to_phys(vectors));

       map.virtual = 0xffff0000;

       map.length = PAGE_SIZE;

       map.type = MT_HIGH_VECTORS;

       create_mapping(&map);

 

       //如果没有配置为高端向量

       if (!vectors_high()) {

              map.virtual = 0;

              map.type = MT_LOW_VECTORS;

              create_mapping(&map);

       }

 

       /*

        * Ask the machine support to map in the statically mapped devices.

        */

        //其实就是调用了iotable_init(sep4020_io_desc, ARRAY_SIZE(sep4020_io_desc))函数

        //而这个iotable_init函数调用了create_mapping这个函数把我们这个数组中的各个成员建立页表;

       if (mdesc->map_io)

              mdesc->map_io();

 

       /*

        * Finally flush the caches and tlb to ensure that we're in a

        * consistent state wrt the writebuffer.  This also ensures that

        * any write-allocated cache lines in the vector page are written

        * back.  After this point, we can start to touch devices again.

        */

        //建立完页表一定要刷tlb,原因见上英文部分

        local_flush_tlb_all();

       flush_cache_all();

}

       //关于pgdpmdpte

       //PGD每个条目中指向一个PUDPUD的每个条目指向

       //一个PMDPMD的每个条目指向一个PTEPTE的每个条目指向一个页面(Page)的物理首地址。

       //arm中没有使用pudpmd也是直接返回的

       //这里就是返回0xffff0000这一页在pgd中的偏移项

       top_pmd = pmd_off_k(0xffff0000);

 

       /*

        * allocate the zero page.  Note that we count on this going ok.

        */

        //empty_zero_page是一中特殊的页,供初始化为0的数据和写时复制(cow)使用

       zero_page = alloc_bootmem_low_pages(PAGE_SIZE);

       memzero(zero_page, PAGE_SIZE);

       empty_zero_page = virt_to_page(zero_page);

       flush_dcache_page(empty_zero_page);

}

 

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