The address in xen

The address in xen

[张琳]

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It seems that the address in xen has three layer: the virtual address , the pesurdo-physical address and the machine address.

I obtained some addresses of kernel symbols by parsing the system.map file.
I think this address is virtual address.Is it correct?
Then I want to calculate the hash value of memory area start from those addresses. So I have to access the corresponding machine address.

Then problem came.
How to translate the virtual address to machine address?

First, I want to translate the virtual address to pesurdo-physical address by traversing page table tree. But segmentation fault always occurs.

I put my code in the following~~~
Can anyone tell me that what is wrong?

unsigned long VAtoPA(unsigned long VirtualAddress)
{
  /*This variable is used for storing the address of    
     the Page Directory.*/
  unsigned long PDAddress; 

  /*This variable is a pointer pointing to the entry 
     in the page directory which contains the address   
     of the Page Table.*/
  unsigned long* pPTAddress;

  /*This variable is used for storing the address of  
     the Page Table.*/
  unsigned long PTAddress;

  /*This variable is a pointer pointing to the entry 
    in the page table which contains the address of 
    the physical page.*/
  unsigned long* pPPAddress;
  
  /*This variable is used for storing the address of 
    the physical page.*/
  unsigned long PPAddress;
  
  /*This is physical address for the corresponding  
     virtual address.*/
  unsigned long PhysicalAddress;

  /*Get the address of the Page Directory from CR3*/
  int xc_handle = xc_interface_open();
  if(xc_handle == -1)
    {
      printf("Sorry! Cannot open an interface on xen 
                hypervisor, please check that whether 
                the xen is running or not!\n");
      exit(1);
    }

  vcpu_guest_context_t context;
  int result = xc_vcpu_getcontext(xc_handle, 
                                         1, 0, &context);
  if(result == -1)
    {
      printf("Sorry! Cannot get the context of the 
                virtual CPU-1 in domain-1, please check 
                that whether the domain-1 is running or 
                not!\n");
      exit(1);
    }
    PDAddress = context.ctrlreg[3] & 0xFFFFF000;
 
  int index;
  /*Get the index number in Page Directory.*/
  index = VirtualAddress >> 22;
  /*Get the address of the entry which contains the 
     address of the Page Table.*/
  pPTAddress = PDAddress + (index << 2);
  /*Get the address of the Page Table*/
  PTAddress = (*pPTAddress) & 0xFFFFF000;
  /*Get the index number in Page Table.*/
  index = (VirtualAddress >> 12) & 0x000003FF;
  /*Get the address of the entry which contains the 
     address of the physical page.*/
  pPPAddress = PTAddress + (index << 2);
  /*Get the address of the physical page.*/
  PPAddress = (*pPPAddress) & 0xFFFFF000;

  PhysicalAddress = PPAddress + (VirtualAddress & 0x00000FFF);


  result = xc_interface_close(xc_handle);
  if(result == -1)
    {
      printf("Sorry! Cannot close the special 
                interface on xen hypervisor!\n");
      exit(1);
    }

  return PhysicalAddress;
} 

 


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Re: The address in xen

[weiming]

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In the xen kernel, there's existing functions/macros to convert between
these addresses.
Your calculation may be not correct. Every address stored in the page
table/directory is machine address. But your pointer should use virtual
address to access them.

weiming

2008/3/17 张琳 <zhanglin_nk@tom.com>:

> It seems that the address in xen has three layer: the virtual address ,
> the pesurdo-physical address and the machine address.
>
> I obtained some addresses of kernel symbols by parsing the system.mapfile.
> I think this address is virtual address.Is it correct?
> Then I want to calculate the hash value of memory area start from those
> addresses. So I have to access the corresponding machine address.
>
> Then problem came.
> How to translate the virtual address to machine address?
>
> First, I want to translate the virtual address to pesurdo-physical address
> by traversing page table tree. But segmentation fault always occurs.
>
> I put my code in the following~~~
> Can anyone tell me that what is wrong?
>
> unsigned long VAtoPA(unsigned long VirtualAddress)
> {
> /*This variable is used for storing the address of
> the Page Directory.*/
> unsigned long PDAddress;
>
> /*This variable is a pointer pointing to the entry
> in the page directory which contains the address
> of the Page Table.*/
> unsigned long* pPTAddress;
>
> /*This variable is used for storing the address of
> the Page Table.*/
> unsigned long PTAddress;
>
> /*This variable is a pointer pointing to the entry
> in the page table which contains the address of
> the physical page.*/
> unsigned long* pPPAddress;
>
> /*This variable is used for storing the address of
> the physical page.*/
> unsigned long PPAddress;
>
> /*This is physical address for the corresponding
> virtual address.*/
> unsigned long PhysicalAddress;
>
> /*Get the address of the Page Directory from CR3*/
> int xc_handle = xc_interface_open();
> if(xc_handle == -1)
> {
> printf("Sorry! Cannot open an interface on xen
> hypervisor, please check that whether
> the xen is running or not!\n");
> exit(1);
> }
>
> vcpu_guest_context_t context;
> int result = xc_vcpu_getcontext(xc_handle,
> 1, 0, &context);
> if(result == -1)
> {
> printf("Sorry! Cannot get the context of the
> virtual CPU-1 in domain-1, please check
> that whether the domain-1 is running or
> not!\n");
> exit(1);
> }
> PDAddress = context.ctrlreg[3] & 0xFFFFF000;
>
> int index;
> /*Get the index number in Page Directory.*/
> index = VirtualAddress >> 22;
> /*Get the address of the entry which contains the
> address of the Page Table.*/
> pPTAddress = PDAddress + (index << 2);
> /*Get the address of the Page Table*/
> PTAddress = (*pPTAddress) & 0xFFFFF000;
> /*Get the index number in Page Table.*/
> index = (VirtualAddress >> 12) & 0x000003FF;
> /*Get the address of the entry which contains the
> address of the physical page.*/
> pPPAddress = PTAddress + (index << 2);
> /*Get the address of the physical page.*/
> PPAddress = (*pPPAddress) & 0xFFFFF000;
>
> PhysicalAddress = PPAddress + (VirtualAddress & 0x00000FFF);
>
>
> result = xc_interface_close(xc_handle);
> if(result == -1)
> {
> printf("Sorry! Cannot close the special
> interface on xen hypervisor!\n");
> exit(1);
> }
>
> return PhysicalAddress;
> }
>
>
>
>
>
>
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