swapper_pg_dir的作用

编程

在内存系统初始化过程中,有如下代码:

   1: static void __init pagetable_init(void)

2: {

3: pgd_t *pgd_base = swapper_pg_dir;

4:

5: permanent_kmaps_init(pgd_base);

6: }

这里,我们看到了神秘的swapper_pg_dir,全局搜索一下,发现了

   1: /*

2: * Build a proper pagetable for the kernel mappings. Up until this

3: * point, we"ve been running on some set of pagetables constructed by

4: * the boot process.

5: *

6: * If we"re booting on native hardware, this will be a pagetable

7: * constructed in arch/x86/kernel/head_32.S. The root of the

8: * pagetable will be swapper_pg_dir.

9: *

10: * If we"re booting paravirtualized under a hypervisor, then there are

11: * more options: we may already be running PAE, and the pagetable may

12: * or may not be based in swapper_pg_dir. In any case,

13: * paravirt_pagetable_setup_start() will set up swapper_pg_dir

14: * appropriately for the rest of the initialization to work.

15: *

16: * In general, pagetable_init() assumes that the pagetable may already

17: * be partially populated, and so it avoids stomping on any existing

18: * mappings.

19: */

20: void __init early_ioremap_page_table_range_init(void)

21: {

22: pgd_t *pgd_base = swapper_pg_dir;

23: unsigned long vaddr, end;

24:

25: /*

26: * Fixed mappings, only the page table structure has to be

27: * created - mappings will be set by set_fixmap():

28: */

29: vaddr = __fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK;

30: end = (FIXADDR_TOP + PMD_SIZE - 1) & PMD_MASK;

31: page_table_range_init(vaddr, end, pgd_base);

32: early_ioremap_reset();

33: }

在head_32.S中,定义了如下的BSS段,BSS段是在内核映像文件中不占空间,但是在内核被加载到内存时,会保留相应的空间。

在BSS段,一共保留了4个页面的空间,分别用initial_page_table, initial_pg_fixmap, empty_zero_page和swapper_pg_dir来标志其地址。

   1: /*

2: * BSS section

3: */

4: __PAGE_ALIGNED_BSS

5: .align PAGE_SIZE

6: #ifdef CONFIG_X86_PAE

7: initial_pg_pmd:

8: .fill 1024*KPMDS,4,0

9: #else

10: ENTRY(initial_page_table)

11: .fill 1024,4,0

12: #endif

13: initial_pg_fixmap:

14: .fill 1024,4,0

15: ENTRY(empty_zero_page)

16: .fill 4096,1,0

17: ENTRY(swapper_pg_dir)

18: .fill 1024,4,0

通过如下代码,将initial_page_table设置为初始页目录

   1: /*

2: * Enable paging

3: */

4: movl $pa(initial_page_table), %eax

5: movl %eax,%cr3 /* set the page table pointer.. */

6: movl %cr0,%eax

7: orl $X86_CR0_PG,%eax

8: movl %eax,%cr0 /* ..and set paging (PG) bit */

9: ljmp $__BOOT_CS,$1f /* Clear prefetch and normalize %eip */

在内核初始化阶段,setup_arch调用了如下的函数:

   1: void __init setup_arch(char **cmdline_p)

2: {

3:

4: ......

5: /* max_pfn_mapped is updated here */

6: max_low_pfn_mapped = init_memory_mapping(0, max_low_pfn<<PAGE_SHIFT);

7: max_pfn_mapped = max_low_pfn_mapped;

8: ......

9: x86_init.paging.pagetable_setup_start(swapper_pg_dir);

10: paging_init();

11: x86_init.paging.pagetable_setup_done(swapper_pg_dir);

12:

13: ......

14: }

init_memory_mapping调用了kernel_physical_mapping_init,初始化swapper_pg_dir

  1: /*

2: * This maps the physical memory to kernel virtual address space, a total

3: * of max_low_pfn pages, by creating page tables starting from address

4: * PAGE_OFFSET:

5: */

6: unsigned long __init

7: kernel_physical_mapping_init(unsigned long start,

8: unsigned long end,

9: unsigned long page_size_mask)

10: {

11: int use_pse = page_size_mask == (1<<PG_LEVEL_2M);

12: unsigned long last_map_addr = end;

13: unsigned long start_pfn, end_pfn;

14: pgd_t *pgd_base = swapper_pg_dir;

15: int pgd_idx, pmd_idx, pte_ofs;

16: unsigned long pfn;

17: pgd_t *pgd;

18: pmd_t *pmd;

19: pte_t *pte;

20: unsigned pages_2m, pages_4k;

21: int mapping_iter;

22:

23: start_pfn = start >> PAGE_SHIFT;

24: end_pfn = end >> PAGE_SHIFT;

25:

26: /*

27: * First iteration will setup identity mapping using large/small pages

28: * based on use_pse, with other attributes same as set by

29: * the early code in head_32.S

30: *

31: * Second iteration will setup the appropriate attributes (NX, GLOBAL..)

32: * as desired for the kernel identity mapping.

33: *

34: * This two pass mechanism conforms to the TLB app note which says:

35: *

36: * "Software should not write to a paging-structure entry in a way

37: * that would change, for any linear address, both the page size

38: * and either the page frame or attributes."

39: */

40: mapping_iter = 1;

41:

42: if (!cpu_has_pse)

43: use_pse = 0;

44:

45: at:

46: pages_2m = pages_4k = 0;

47: pfn = start_pfn;

48: pgd_idx = pgd_index((pfn<<PAGE_SHIFT) + PAGE_OFFSET);

49: pgd = pgd_base + pgd_idx;

50: for (; pgd_idx < PTRS_PER_PGD; pgd++, pgd_idx++) {

51: pmd = one_md_table_init(pgd);

52:

53: if (pfn >= end_pfn)

54: continue;

55: ef CONFIG_X86_PAE

56: pmd_idx = pmd_index((pfn<<PAGE_SHIFT) + PAGE_OFFSET);

57: pmd += pmd_idx;

58: e

59: pmd_idx = 0;

60: if

61: for (; pmd_idx < PTRS_PER_PMD && pfn < end_pfn;

62: pmd++, pmd_idx++) {

63: unsigned int addr = pfn * PAGE_SIZE + PAGE_OFFSET;

64:

65: /*

66: * Map with big pages if possible, otherwise

67: * create normal page tables:

68: */

69: if (use_pse) {

70: unsigned int addr2;

71: pgprot_t prot = PAGE_KERNEL_LARGE;

72: /*

73: * first pass will use the same initial

74: * identity mapping attribute + _PAGE_PSE.

75: */

76: pgprot_t init_prot =

77: __pgprot(PTE_IDENT_ATTR |

78: _PAGE_PSE);

79:

80: addr2 = (pfn + PTRS_PER_PTE-1) * PAGE_SIZE +

81: PAGE_OFFSET + PAGE_SIZE-1;

82:

83: if (is_kernel_text(addr) ||

84: is_kernel_text(addr2))

85: prot = PAGE_KERNEL_LARGE_EXEC;

86:

87: pages_2m++;

88: if (mapping_iter == 1)

89: set_pmd(pmd, pfn_pmd(pfn, init_prot));

90: else

91: set_pmd(pmd, pfn_pmd(pfn, prot));

92:

93: pfn += PTRS_PER_PTE;

94: continue;

95: }

96: pte = one_page_table_init(pmd);

97:

98: pte_ofs = pte_index((pfn<<PAGE_SHIFT) + PAGE_OFFSET);

99: pte += pte_ofs;

100: for (; pte_ofs < PTRS_PER_PTE && pfn < end_pfn;

101: pte++, pfn++, pte_ofs++, addr += PAGE_SIZE) {

102: pgprot_t prot = PAGE_KERNEL;

103: /*

104: * first pass will use the same initial

105: * identity mapping attribute.

106: */

107: pgprot_t init_prot = __pgprot(PTE_IDENT_ATTR);

108:

109: if (is_kernel_text(addr))

110: prot = PAGE_KERNEL_EXEC;

111:

112: pages_4k++;

113: if (mapping_iter == 1) {

114: set_pte(pte, pfn_pte(pfn, init_prot));

115: last_map_addr = (pfn << PAGE_SHIFT) + PAGE_SIZE;

116: } else

117: set_pte(pte, pfn_pte(pfn, prot));

118: }

119: }

120: }

121: if (mapping_iter == 1) {

122: /*

123: * update direct mapping page count only in the first

124: * iteration.

125: */

126: update_page_count(PG_LEVEL_2M, pages_2m);

127: update_page_count(PG_LEVEL_4K, pages_4k);

128:

129: /*

130: * local global flush tlb, which will flush the previous

131: * mappings present in both small and large page TLB"s.

132: */

133: __flush_tlb_all();

134:

135: /*

136: * Second iteration will set the actual desired PTE attributes.

137: */

138: mapping_iter = 2;

139: goto repeat;

140: }

141: return last_map_addr;

142: }

pgd_t *pgd_base = swapper_pg_dir;

将swapper_pg_dir作为页目录地址,赋给pgd_base

start_pfn = start >> PAGE_SHIFT;

end_pfn = end >> PAGE_SHIFT;

pgd_idx = pgd_index((pfn<<PAGE_SHIFT) + PAGE_OFFSET);

pgd = pgd_base + pgd_idx;

pgd_idx,pgd代表着在页目录中的索引,以及相应的页目录项

  1: pgprot_t prot = PAGE_KERNEL;

2: /*

3: * first pass will use the same initial

4: * identity mapping attribute.

5: */

6: pgprot_t init_prot = __pgprot(PTE_IDENT_ATTR);

7:

8: if (is_kernel_text(addr))

9: prot = PAGE_KERNEL_EXEC;

10:

11: pages_4k++;

12: if (mapping_iter == 1) {

13: set_pte(pte, pfn_pte(pfn, init_prot));

14: last_map_addr = (pfn << PAGE_SHIFT) + PAGE_SIZE;

15: } else

16: set_pte(pte, pfn_pte(pfn, prot));

最后,通过两个回合的遍历,将属性设置到对应的页表项上去。

以上是 swapper_pg_dir的作用 的全部内容, 来源链接: utcz.com/z/516157.html

回到顶部