用户空间的虚拟地址如何转换得到实际的物理地址

思路：

进程号是一个进程在用户空间的唯一标示，所以，根据pid可以从内核中得到一个进程的所有信息，

另外就是知道虚拟地址就可以通过内核物理地址映射到虚拟地址的逆运算就可以还原他的实际物理地址

以上便是虚拟地址转换成所对应的实际物理地址的思路。

大致的代码编写流程：

代码：

#include <linux/sched.h> 
#include <linux/mm.h> 
#include <asm/pgtable.h> 
#include <asm/page.h> 
 
static int v2p(int pid, unsigned long va) 
{ 
    unsigned long pa = 0; 
    struct task_struct *pcb_tmp; 
    pgd_t *pgd_tmp = NULL; 
    pud_t *pud_tmp = NULL; 
    pmd_t *pmd_tmp = NULL; 
    pte_t *pte_tmp = NULL; 
 
    printk(KERN_INFO"PAGE_OFFSET = 0x%lx\n",PAGE_OFFSET); 
    printk(KERN_INFO"PGDIR_SHIFT = %d\n",PGDIR_SHIFT); 
    printk(KERN_INFO"PUD_SHIFT = %d\n",PUD_SHIFT); 
    printk(KERN_INFO"PMD_SHIFT = %d\n",PMD_SHIFT); 
    printk(KERN_INFO"PAGE_SHIFT = %d\n",PAGE_SHIFT); 
 
    printk(KERN_INFO"PTRS_PER_PGD = %d\n",PTRS_PER_PGD); 
    printk(KERN_INFO"PTRS_PER_PUD = %d\n",PTRS_PER_PUD); 
    printk(KERN_INFO"PTRS_PER_PMD = %d\n",PTRS_PER_PMD); 
    printk(KERN_INFO"PTRS_PER_PTE = %d\n",PTRS_PER_PTE); 
 
    printk(KERN_INFO"PAGE_MASK = 0x%lx\n",PAGE_MASK); 
 /* 查询当前进程下的虚拟地址 */
 //   pcb_tmp = current; 
/* 查询指定进程的下的虚拟地址 */
     pcb_tmp = find_task_by_vpid (pid); // 较新一点的内核版本使用这个函数
// pcb_tmp = find_task_by_pid (pid);    // 旧版本的内核版本使用这个函数
    printk(KERN_INFO"pgd = 0x%p\n",pcb_tmp->mm->pgd); 
    if(!find_vma(pcb_tmp->mm,va)){ 
                    printk(KERN_INFO"virt_addr 0x%lx not available.\n",va); 
                    return 0; 
    } 
    pgd_tmp = pgd_offset(pcb_tmp->mm,va); 
    printk(KERN_INFO"pgd_tmp = 0x%p\n",pgd_tmp); 
    printk(KERN_INFO"pgd_val(*pgd_tmp) = 0x%lx\n",pgd_val(*pgd_tmp)); 
    if(pgd_none(*pgd_tmp)){ 
                    printk(KERN_INFO"Not mapped in pgd.\n");                 
                    return 0; 
    } 
    pud_tmp = pud_offset(pgd_tmp,va); 
    printk(KERN_INFO"pud_tmp = 0x%p\n",pud_tmp); 
    printk(KERN_INFO"pud_val(*pud_tmp) = 0x%lx\n",pud_val(*pud_tmp)); 
    if(pud_none(*pud_tmp)){ 
                    printk(KERN_INFO"Not mapped in pud.\n"); 
                    return 0; 
    } 
    pmd_tmp = pmd_offset(pud_tmp,va); 
    printk(KERN_INFO"pmd_tmp = 0x%p\n",pmd_tmp); 
    printk(KERN_INFO"pmd_val(*pmd_tmp) = 0x%lx\n",pmd_val(*pmd_tmp)); 
    if(pmd_none(*pmd_tmp)){ 
                    printk(KERN_INFO"Not mapped in pmd.\n"); 
                    return 0; 
    } 
 
    pte_tmp = pte_offset_kernel(pmd_tmp,va); 
 
    printk(KERN_INFO"pte_tmp = 0x%p\n",pte_tmp); 
    printk(KERN_INFO"pte_val(*pte_tmp) = 0x%lx\n",pte_val(*pte_tmp)); 
    if(pte_none(*pte_tmp)){ 
                    printk(KERN_INFO"Not mapped in pte.\n"); 
                    return 0; 
    } 
    if(!pte_present(*pte_tmp)){ 
                    printk(KERN_INFO"pte not in RAM.\n"); 
                    return 0; 
    } 
    pa = (pte_val(*pte_tmp) & PAGE_MASK) |(va & ~PAGE_MASK); 
    printk(KERN_INFO"virt_addr 0x%lx in RAM is 0x%lx .\n",va,pa); 
    printk(KERN_INFO"contect in 0x%lx is 0x%lx\n",pa, 
                    *(unsigned long *)((char *)pa + PAGE_OFFSET)); 
                           
}