[lab2:Memory Management][实现]kern/pmap.c重要函数(2)

1、pgdir_walk()，返回指向为线性地址va分配的页表入口地址。如果相关页表没有在页目录中，那么做如下工作：

   如果create为0，那么返回NULL。否则，pgdir_walk()用page_alloc()分配一个新页，将pp_ref设置为1

===============================code=====================================

pte_t *
pgdir_walk(pde_t *pgdir, const void *va, int create)
{
 // Fill this function in       
      //
      // +--------10------+-------10-------+---------12----------+
      // | Page Directory |   Page Table   | Offset within Page  |
      // |      Index     |      Index     |                     |
      // +----------------+----------------+---------------------+
      //  \--- PDX(la) --/ \--- PTX(la) --/ \---- PGOFF(la) ----/
      //  \----------- PPN(la) -----------/
     
 struct Page* p;
 pte_t *pt;

 pgdir = (pde_t *)&pgdir[PDX(va)];
 //whether the page table exist or not
 //it isn't exist~ 
 if(0 == (*pgdir& PTE_P)){
  if(0 == create)return NULL;
  //allocate a page
  if(page_alloc(&p) < 0)return NULL;
  //p points to an entry in the pages table and set pp_ref to 1
  p->pp_ref = 1;
  //set the page clear
  memset(KADDR(page2pa(p)), 0, PGSIZE);
  //make the page directory point to that page (contains pt)
  *pgdir = page2pa(p) | PTE_U |PTE_W | PTE_P;
  }
 pt = (pte_t*) KADDR(PTE_ADDR(*pgdir));
 
 // Page table exists, return the VA of the page table entry
 return &pt[PTX(va)];
}

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2、boot_map_segment()，将[la, la+size)的线性地址映射到[pa, pa+size)的物理地址上：

===============================code=====================================

static void
boot_map_segment(pde_t *pgdir, uintptr_t la, size_t size, physaddr_t pa, int perm)
{
 // Fill this function in
 uintptr_t i;
 pte_t *p;
 
 //1)Size is a multiple of PGSIZE and la must be a multiple of PGSIZE
 size = ROUNDUP(size, PGSIZE);
 assert (0 == la % PGSIZE); //assert va is a multiple of BY2PG.

 //2)size is multiple of PGSIZE,so we should creat pages no less 1
 for(i = 0; i < size; i+=PGSIZE){
  p = pgdir_walk(pgdir, (void*)la + i, 1);
  assert(p != NULL);
  *p = (pa +i) |perm |PTE_P;
  }//end for
 
}

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3、page_lookup()，返回在虚拟地址va处分配的页面。

===============================code=====================================

struct Page *
page_lookup(pde_t *pgdir, void *va, pte_t **pte_store)
{
 // Fill this function in
 //pte is the pointer to the page table entry for va
 pte_t *pte = pgdir_walk(pgdir, va, 0);
 if(NULL == pte)
  return NULL;
 
  // If pte_store is not zero, then we store in it the address
   // of the pte for that page
 if(pte_store != NULL)
  *pte_store = pte;

 return pa2page(*pte); 
}

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4、page_remove()：

===============================code=====================================

void
page_remove(pde_t *pgdir, void *va)
{
 // Fill this function in

 pte_t *pte = NULL;
 struct Page *p;
 
 p = page_lookup(pgdir, va, &pte);
 if(NULL == p) return;
 //The ref count on the physical page should decrement
 page_decref(p);

 // Set the respective page table entry to 0
   if(pte != NULL)
      *pte = 0;
 //Set the TLB invalid
 tlb_invalidate(pgdir,  va);
 
}

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5、page_insert()

===============================code=====================================

int
page_insert(pde_t *pgdir, struct Page *pp, void *va, int perm)
{
 // Fill this function in
 pte_t *pte;
 
 pte = pgdir_walk(pgdir, va, 1);
 if(NULL == pte)
  return -E_NO_MEM;
 // First increase the reference count so the page doesn't get
 // removed in the next step if we try to repeat a mapping
  pp->pp_ref++;

 // If there is something mapped there, page remove it
 if( (*pte & PTE_P) != 0)
  page_remove(pgdir, va);
 
 *pte = page2pa(pp) |PTE_P |perm;
 
 return 0;
}

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6、补全i386_vm_init()

===============================code=====================================

void
i386_vm_init(void)

{

......
 //////////////////////////////////////////////////////////////////////
 // Map 'pages' read-only by the user at linear address UPAGES
 // (ie. perm = PTE_U | PTE_P)
 // Permissions:
 //    - pages -- kernel RW, user NONE
 //    - the read-only version mapped at  -- kernel R, user R
 // Your code goes here:
 n = ROUNDUP(npage*sizeof(struct Page), PGSIZE);
 assert(n < 4 *1024 * 1024);
 boot_map_segment(pgdir, UPAGES, n,
      PADDR(pages),PTE_W |PTE_U);

 //////////////////////////////////////////////////////////////////////
 // Map the kernel stack (symbol name "bootstack").  The complete VA
 // range of the stack, [KSTACKTOP-PTSIZE, KSTACKTOP), breaks into two
 // pieces:
 //     * [KSTACKTOP-KSTKSIZE, KSTACKTOP) -- backed by physical memory
 //     * [KSTACKTOP-PTSIZE, KSTACKTOP-KSTKSIZE) -- not backed => faults
 //     Permissions: kernel RW, user NONE
 // Your code goes here:
 boot_map_segment(pgdir, KSTACKTOP-KSTKSIZE, KSTKSIZE,
      PADDR(bootstack), PTE_W |PTE_P)
 boot_map_segment(pgdir, KSTACKTOP-PTSIZE, PTSIZE-KSTKSIZE, 0, 0);

 

 //////////////////////////////////////////////////////////////////////
 // Map all of physical memory at KERNBASE.
 // Ie.  the VA range [KERNBASE, 2^32) should map to
 //      the PA range [0, 2^32 - KERNBASE)
 // We might not have 2^32 - KERNBASE bytes of physical memory, but
 // we just set up the amapping anyway.
 // Permissions: kernel RW, user NONE
 // Your code goes here:
 boot_map_segment(pgdir, KERNBASE, ~KERNBASE+1,0, PTE_W|PTE_P);

......

}

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