【轉】creat_mapping

http://blog.csdn.net/huyugv_830913/article/details/5884628

 

1 ARM920T的MMU工作原理

 

下圖顯示了MMU地址轉化關係

一級表項的地址(pmd) = ( (TLB) & (0xFFFFC000) ) + ( (Table Index)<<2 );

注1：TLB(Translate table base),即轉換表基地址

注2：由於每個表項佔32位(4Bytes),因此(Table Index)<<2

一級表項的內容(*pmd) = ( (pte) & (0xFFFFFC00) ) + prot_l1;

-------------------------------------------------------------------------------------

二級表項的地址(pte) =  ( (pte) & (0xFFFFFC00) )  + ( (L2 table index) <<2 );

二級表項的內容(*pte) = ( (PA) & (0xFFFFF000) ) + prot_pte;





2 create_mapping分析
//利用該函數可以爲物理地址創建內存的靜態映射

static void __init create_mapping(struct map_desc *md)
{
     ...  

     pgd = pgd_offset_k(addr);

     //計算pgd的地址(64bits) = ((mm)->pgd+pgd_index(addr))

     //                              = ((mm)->pgd+((addr) >> 21) )

     //pmd地址(32bits)        = ((mm)->pgd+((addr) >> 20) )

     end = addr + length;

     //PGDIR_SIZE=(1UL << PGDIR_SHIFT)=2M

     //一次處理2個連續的一級表項:2*1M = 2M
     do {
            unsigned long next = pgd_addr_end(addr, end);

            alloc_init_section(pgd, addr, next, phys, type);

            phys += next - addr;
            addr = next;
      } while (pgd++, addr != end);
}



//嘗試使用段映射

static void __init alloc_init_section(pgd_t *pgd, unsigned long addr,
          unsigned long end, unsigned long phys,
          const struct mem_type *type)
{
     pmd_t *pmd = pmd_offset(pgd, addr); //一級表指針

     //pmd地址(32bits)        = ((mm)->pgd+((addr) >> 20) )

     

     /*  當大小和地址1MB對齊時，使用段映射 */
     if (((addr | end | phys) & ~SECTION_MASK) == 0) {
         pmd_t *p = pmd;

         if (addr & SECTION_SIZE)
              pmd++;

         do {
             *pmd = __pmd(phys | type->prot_sect);
             phys += SECTION_SIZE;
         } while (pmd++, addr += SECTION_SIZE, addr != end);

         //2MB,循環2次

         flush_pmd_entry(p);
      } else {
          /*  使用small頁映射，必須爲二級表分配空間4Kb(1page) */
          alloc_init_pte(pmd, addr, end, __phys_to_pfn(phys), type);
       }
}



//small頁映射

static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
      unsigned long end, unsigned long pfn,
      const struct mem_type *type)
{
     pte_t *pte;  //二級表指針

     

     //當一級表項內容爲空時,爲二級表項分配空間2*512*4 = 4Kb(1Page)

     if (pmd_none(*pmd)) {
         pte = alloc_bootmem_low_pages(2 * PTRS_PER_PTE * sizeof(pte_t));
          __pmd_populate(pmd, __pa(pte) | type->prot_l1);

         //給一級表項賦值，pmd爲指針，指向需賦值的地址

         //pmdp[0] = __pmd(pmdval);
         //pmdp[1] = __pmd(pmdval + 256 * sizeof(pte_t));



      }

      pte = pte_offset_kernel(pmd, addr);
      do {
          set_pte_ext(pte, pfn_pte(pfn, __pgprot(type->prot_pte)), 0);
          pfn++;
      } while (pte++, addr += PAGE_SIZE, addr != end);

      //2MB,2Mb/4Kb = 512次(最多)
}







.macro armv3_set_pte_ext wc_disable=1
 str r1, [r0], #-2048  @ linux version  MMU看到的h/w pte0/1

 eor r3, r1, #L_PTE_PRESENT | L_PTE_YOUNG | L_PTE_WRITE | L_PTE_DIRTY

 bic r2, r1, #PTE_SMALL_AP_MASK @ keep C, B bits
 bic r2, r2, #PTE_TYPE_MASK
 orr r2, r2, #PTE_TYPE_SMALL

 tst r3, #L_PTE_USER   @ user?
 orrne r2, r2, #PTE_SMALL_AP_URO_SRW  @設置SVC模式爲讀寫，USR模式爲READONLY

 tst r3, #L_PTE_WRITE | L_PTE_DIRTY @ write and dirty?
 orreq r2, r2, #PTE_SMALL_AP_UNO_SRW 

設置SVC模式爲讀寫，USR模式爲不能讀，PTE_SMALL_AP_URO_SRW | PTE_SMALL_AP_UNO_SRW爲SVC & USR可讀寫

#define PAGE_SHARED __pgprot(pgprot_val(pgprot_user) | _L_PTE_READ | \
     L_PTE_WRITE)

#define _L_PTE_READ L_PTE_USER | L_PTE_EXEC

PAGE_SHARED 使用PAGE_SHARE映射的空間USR模式也能進行讀寫

關於讀寫的權限，參考ARM V5 reference.pdf  協處理器的C3寄存器和PTE的APx（3~0），PMD的domain參數

 tst r3, #L_PTE_PRESENT | L_PTE_YOUNG @ present and young?
 movne r2, #0

 .if /wc_disable
#ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
 tst r2, #PTE_CACHEABLE
 bicne r2, r2, #PTE_BUFFERABLE
#endif
 .endif
 str r2, [r0]   @ hardware version
 .endm

 

3 Linux MMU

#define PTRS_PER_PTE512 { (h/w + s/w )  *  4byte = 4096 }
#define PTRS_PER_PMD 1
#define PTRS_PER_PGD 2048

4 9260EK 內存映射情況