[Xen-devel] Re: Mapping foreign frames from dom0

[Julian Stecklina <der_julian@xxxxxx>]

Grzegorz Milos wrote:
> > Hello,
> >
> > I am hacking on a Mini-OS that is able to run as domain 0 and is able 
> > to start a guest (another Mini-OS for now). I was able to get a memory 
> > allocated to the guest and am now trying to build its pagetable and 
> > after that copy the kernel to the right places. The problem is:
> > Given a machine frame number from a memory frame of the guest, how do 
> > I conceptionally map this into dom0's address space? I followed the 
> > code path from xc_map_foreign_range to some obscure pagetable updates 
> > in the Linux kernel, but am still unable to make heads or tails of it.
> > Any help is appreciated.
> Foreign mappings are very similar to standard mappings (assuming that 
> the mapping domain is privileged). HYPERVISOR_mmu_update with domid set 
> to the foreign domain will deal with page table update.
> Note that you need to find some virtual address for the mapping. This is 
> what demand_map_area is for, have a look at map_frames() in 
> arch/x86/mm.c for more info.
Ah, i was under the false impression that I had to modify the MACHPHYS 
table, but doing a normal page table update with the foreigndom set, 
works. Thanks.
Regards,
Julian


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