Re: [Xen-devel] pfn to mfn mapping for HVM domains?

["Bryan D. Payne" <bryan@xxxxxxxxxxxx>]

> thing in PV domains.  Try using xc_translate_gpfn_list instead, which
> does P2M translation on HVM domains.
I'm having trouble with the value returned from this function.  I've  
been working on this for a while and my conclusion is that there must  
be an error in my logic (most likely!) or a bug in this function.   
Perhaps someone could help me figure out which it is...
These are the steps that I'm taking:

* Assume that I have an HVM domain running fedora core 5.  My goal is  
to view the memory page holding the symbol swapper_pg_dir (the kernel  
page global directory, or kpgd for short).
* I lookup the virtual address for kpgd in the System.map file

* I subtract 0xc0000000 from the virtual address to get the physical  
address (which should be valid since this is kernel memory and the  
PAGE_OFFSET for this kernel is 0xc0000000).
* I convert the physical address to a pfn by bit shifting PAGE_SHIFT  
bits to the right
* I translate the pfn to a mfn using the  
xc_domain_translate_gpfn_list function
* I mmap the mfn using xc_map_foreign_range

After doing this, the page that is returned from xc_map_foreign_range  
does not appear to be the correct page.  The offset where the kpgd  
should be located contains all zeros, which can't be correct.
I've tried the same steps with other kernel symbols as well.  Each  
time I get a valid mfn returned by xc_domain_translate_gpfn_list.   
But each time when I map this mfn, the expected information is not on  
that page, so I conclude that the mfn is not correct.
With the exception of the pfn to mfn conversion step, I can do the  
exact same steps on a PV domain and it works every time.  So I'm  
inclined to think that my logic for converting a virtual address to a  
pfn is valid.  Does this imply that there's a bug in  
xc_domain_translate_gpfn_list or am I misinterpreting the function's  
output?
Thanks,
bryan


-
Bryan D. Payne
Graduate Student, Computer Science
Georgia Tech Information Security Center
http://www.bryanpayne.org




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