[Xen-devel] question about gpfn and gmfn

[tgh <tianguanhua@xxxxxxxxxx>]

hi
I try to understand the code of xen memory ,and I am confused  about  
gmfn, gpfn and pfn  in the xen
and in the /xen/include/xen/mm.h  there are some explanation about them 
as follows:
* 1. gpfn/gpaddr: A guest-specific pseudo-physical frame number or address.
* 2. gmfn/gmaddr: A machine address from the p.o.v. of a particular guest.
* 3. mfn/maddr:   A real machine frame number or address.
* 4. pfn/paddr:   Used in 'polymorphic' functions that work across all
*                 address spaces, depending on context. See the pagetable
*                 conversion macros in asm-x86/page.h for examples.
*                 Also 'paddr_t' is big enough to store any physical 
address.
*

last week,I thought I understood the meaning about the gpfn and gmfn,but 
when I  reread  it ,I  find  I do not
I usually think the gpfn/gpaddr is just the gmfn ,that is, 
guest-specific pseudo-physical frame number is just machine address from 
the p.o.v. of a particular guest
I am confused about why does guest-specific pseudo-physical frame 
number  not  equal to machine address from the p.o.v. of a particular guest?
could you help me
Thanks in advance


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