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[Xen-devel] Accessing Dom0 Physical memory from xen, via direct mappings (PML4:262-271)

In config.h (include/asm-x86/config.h) I found this:

#if __x86_64__
 *  0xffff830000000000 - 0xffff87ffffffffff [5TB, 5*2^40 bytes, PML4:262-271]   
 *    1:1 direct mapping of all physical memory.                   

I was wondering if it's possible for dom0 to malloc a huge chunk of memory 
and let xen know the starting address of this range. 
Inside xen, I can translate dom0 virt address to a virt address in the above 
range and access the entire chunk via these virtual addresses.

The catch here is that I want this virtual address range to be accessible 
across all vcpu contexts in xen (whether it's servicing a hypercall from dom0
or a vmx fault caused by Guest).

So far, I have only been able to achieve the former. In the latter case,
where the "current" vcpu belongs to a guest (eg in a vmx fault handler),
I can't access this address range inside xen. Do I have to add EPT
mappings to guest's p2m to do this ? Or can I do something else ?


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