[Xen-devel] Re: Question about xc_ptrace and PV domU process memory map.

[Necrosoft <necrosoft82@xxxxxxxx>]

> You mean xc_ptrace ?  I think these functions are designed only to be
> used following PTRACE_ATTACH.  PTRACE_ATTACH will pause the target
> domain, which may not be what you want.
yes xc_ptrace. Can be ok pause the domU.

> http://xenaccess.sourceforge.net/ may be more what you want.  (I have
> no knowledge of whether XenAccess is any good - I just saw the link
> from wiki.xensource.com.)
I look this...the portions of code about mapping virt. address seem 
quite similar...
> If you want to use libxc you will have to put up with pausing the
> domain, or do some work on the races which result from allowing it to
> run: by my reading of the code it's not correct to arrange to skip the
> pause, or unpause the domain after PTRACE_ATTACH, because
> xc_ptrace.c:map_domain_va assumes that the domain does not allocate
> additional pages between its calls to xc_get_tot_pages and
> xc_get_pfn_list.
So yes, in this week I look better the code and in effect fails for 
incorrect current_domid. Now I did another test:
1. Run in domU a test program, I take a virtual address (for example in 
hex format). This program enter in active waiting and so I pause the 
domain. cr3, now, is relative to PGD for this program.
2. Now I call map_dom_va passing the virtual address described above. 
This function call map_dom_va_32 but this fails at l2e entry retrieve. 
In particular is verified the guard:
if( !(l2e & _PAGE_PRESENT) ) { return NULL; }

So l2e is 0, while l2 is a valid address mapped with 
xc_map_foreign_range. Can you suggest some ideas concerning this type of 
failure?
Thanks

Best Regards

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