Hello,
I was wondering if someone could point me to some documentation that
explains the basic non-nested-paging shadow page table
algorithm/strategy used by KVM. I understand that KVM caches shadow
page tables across context switches and that there is a reverse mapping
and page protection to help zap shadow page tables when the guest page
tables change. However, I'm not entirely sure how the actual caching is
done. At first I assumed that KVM would change the host CR3 on every
guest context switch such that it would point to a cached shadow page
table for the currently running guest user thread, however, as far as I
can tell, the host CR3 does not change so I'm a little lost. If indeed
it doesn't change the CR3, how does KVM solve the problem that arises
when two processes in the guest OS share the same guest logical addresses?
I'm also interested in figuring out what KVM does when running with
multiple virtual CPUs. Looking at the code, I can see that each VCPU
has its own root pointer to a shadow page table graph, but I have yet to
figure out if this graph has node's shared between VCPUs, or whether
they are all private.
Any help would be greatly appreciated. Thanks!
Marek
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