[Xen-devel] Question about monitor_table

[Travis Johnson <tjohnson@xxxxxxxxxxxxxxxx>]

Note: If I don't specify then I'm referring to x86_32 (no PAE). Also I'm 
reading code from the 3.0 release but the concepts are probably the same.
Could someone help me understand the need for the monitor page table. I
figure that arch_vcpu->guest_table points to a guests L2 page table (PD 
on x86) and arch_vcpu->shadow_table points to the guest_table's shadow 
table (if shadowing is turned on) but I don't quite get the purpose of 
the monitor_table. On x86_32 it seems like it just gets set to the value 
of the guest table on initialization and I lose track of it after that. 
I understand Xen needs to trap page table updates but I figured that 
would be a privileged operation and Xen could trap those accesses 
through hardware faults or by paravirtualizing through hypercalls 
(do_mmu_update).
That's a large amount of figuring so if someone could shed some light on 
the purpose and use of the monitor table I would appreciate it.
Xen is awesome.

-Travis


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