|
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 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 //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 //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.prot_l1) mem_types.prot_l1 |= PMD_BIT4; if (mem_types.prot_sect) mem_types.prot_sect |= PMD_BIT4; } } //我们的cachepolicy是3，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 //这里依次获取16个默认的保护类型的值 unsigned long v = pgprot_val(protection_map); //(L_PTE_BUFFERABLE|L_PTE_CACHEABLE)这是linux pte的定义 //内核中有linux和hardware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 = __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——0；user——1；io——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 nr_banks; i++) if (mi->bank.size == 0 || mi->bank.node >= MAX_NUMNODES) mi->bank.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_START是0xc0000000-16M; 以2M为单位，清除内核空间一下的用户空间 for (addr = 0; addr //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 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 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 /* * 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pgd，pmd，pte //PGD每个条目中指向一个PUD，PUD的每个条目指向 //一个PMD，PMD的每个条目指向一个PTE，PTE的每个条目指向一个页面(Page)的物理首地址。 //在arm中没有使用pud，pmd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); } |
|
|
来自： langhuayipian > 《linux内核》
