Linux內核高端內存管理之固定內存區與映射

前面（見 http://www.linuxidc.com/Linux/2012-02/53457.htm 與 http://www.linuxidc.com/Linux/2012-02/53458.htm）總結了高端內存中永久內核映射和臨時內核映射。linux高端內存中的臨時內存區為固定內存區的一部分，下面是Linux內存布局圖

對於固定內存在linux內核中有下面描述

1. enum fixed_addresses {
2. #ifdef CONFIG_X86_32
3. FIX_HOLE,
4. FIX_VDSO,
5. #else
6. VSYSCALL_LAST_PAGE,
7. VSYSCALL_FIRST_PAGE = VSYSCALL_LAST_PAGE
8. + ((VSYSCALL_END-VSYSCALL_START) >> PAGE_SHIFT) - 1,
9. VSYSCALL_HPET,
10. #endif
11. FIX_DBGP_BASE,
12. FIX_EARLYCON_MEM_BASE,
13. #ifdef CONFIG_X86_LOCAL_APIC
14. FIX_APIC_BASE, /* local (CPU) APIC) -- required for SMP or not */
15. #endif
16. #ifdef CONFIG_X86_IO_APIC
17. FIX_IO_APIC_BASE_0,
18. FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS - 1,
19. #endif
20. #ifdef CONFIG_X86_VISWS_APIC
21. FIX_CO_CPU, /* Cobalt timer */
22. FIX_CO_APIC, /* Cobalt APIC Redirection Table */
23. FIX_LI_PCIA, /* Lithium PCI Bridge A */
24. FIX_LI_PCIB, /* Lithium PCI Bridge B */
25. #endif
26. #ifdef CONFIG_X86_F00F_BUG
27. FIX_F00F_IDT, /* Virtual mapping for IDT */
28. #endif
29. #ifdef CONFIG_X86_CYCLONE_TIMER
30. FIX_CYCLONE_TIMER, /*cyclone timer register*/
31. #endif
32. #ifdef CONFIG_X86_32
33. FIX_KMAP_BEGIN, /* reserved pte's for temporary kernel mappings */
34. FIX_KMAP_END = FIX_KMAP_BEGIN+(KM_TYPE_NR*NR_CPUS)-1,
35. #ifdef CONFIG_PCI_MMCONFIG
36. FIX_PCIE_MCFG,
37. #endif
38. #endif
39. #ifdef CONFIG_PARAVIRT
40. FIX_PARAVIRT_BOOTMAP,
41. #endif
42. FIX_TEXT_POKE1, /* reserve 2 pages for text_poke() */
43. FIX_TEXT_POKE0, /* first page is last, because allocation is backward */
44. __end_of_permanent_fixed_addresses,
45. /*
46. * 256 temporary boot-time mappings, used by early_ioremap(),
47. * before ioremap() is functional.
48. *
49. * We round it up to the next 256 pages boundary so that we
50. * can have a single pgd entry and a single pte table:
51. */
52. #define NR_FIX_BTMAPS 64
53. #define FIX_BTMAPS_SLOTS 4
54. FIX_BTMAP_END = __end_of_permanent_fixed_addresses + 256 -
55. (__end_of_permanent_fixed_addresses & 255),
56. FIX_BTMAP_BEGIN = FIX_BTMAP_END + NR_FIX_BTMAPS*FIX_BTMAPS_SLOTS - 1,
57. #ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
58. FIX_OHCI1394_BASE,
59. #endif
60. #ifdef CONFIG_X86_32
61. FIX_WP_TEST,
62. #endif
63. #ifdef CONFIG_INTEL_TXT
64. FIX_TBOOT_BASE,
65. #endif
66. __end_of_fixed_addresses
67. };

固定映射

ioremap的作用是將IO和BIOS以及物理地址空間映射到在896M至1G的128M的地址空間內，使得kernel能夠訪問該空間並進行相應的讀寫操作。

start_kernel()->setup_arch()->early_ioremap_init()

1. void __init early_ioremap_init(void)
2. {
3. pmd_t *pmd;
4. int i;
6. if (early_ioremap_debug)
7. printk(KERN_INFO "early_ioremap_init()\n");
8. /*將fixed_address裡的索引的虛擬地址放入slot_virt
9. ，從代碼裡面可以看出，放入slot_virt中得虛擬地址為1M*/
10. for (i = 0; i < FIX_BTMAPS_SLOTS; i++)
11. slot_virt[i] = __fix_to_virt(FIX_BTMAP_BEGIN - NR_FIX_BTMAPS*i);
13. /*得到固定映射區的pmd
14. ，此pmd為虛擬地址轉換為物理地址的pmd*/
15. pmd = early_ioremap_pmd(fix_to_virt(FIX_BTMAP_BEGIN));
16. memset(bm_pte, 0, sizeof(bm_pte));
17. /*將bm_pte頁表設置為固定映射區開始地址的pmd的第一個頁表；*/
18. pmd_populate_kernel(&init_mm, pmd, bm_pte);
20. /*
21. * The boot-ioremap range spans multiple pmds, for which
22. * we are not prepared:
23. */
24. /*系統要求所有的ioremap映射在一個pmd上，超出這個pmd將警告*/
25. if (pmd != early_ioremap_pmd(fix_to_virt(FIX_BTMAP_END))) {
26. WARN_ON(1);
27. printk(KERN_WARNING "pmd %p != %p\n",
28. pmd, early_ioremap_pmd(fix_to_virt(FIX_BTMAP_END)));
29. printk(KERN_WARNING "fix_to_virt(FIX_BTMAP_BEGIN): %08lx\n",
30. fix_to_virt(FIX_BTMAP_BEGIN));
31. printk(KERN_WARNING "fix_to_virt(FIX_BTMAP_END): %08lx\n",
32. fix_to_virt(FIX_BTMAP_END));
34. printk(KERN_WARNING "FIX_BTMAP_END: %d\n", FIX_BTMAP_END);
35. printk(KERN_WARNING "FIX_BTMAP_BEGIN: %d\n",
36. FIX_BTMAP_BEGIN);
37. }
38. }

1. static unsigned long slot_virt[FIX_BTMAPS_SLOTS] __initdata;

1. #define __fix_to_virt(x) (FIXADDR_TOP - ((x) << PAGE_SHIFT))

其中FIXADDR_TOP為4G-4K。