Hi all,
I was reading the "The shadowy depths of the KVM MMU" presentation by
Avi Kivity.
From my understanding of shadow page-table,
Guest Page Table : maps GV -> GP
Shadow Page Table : maps GV -> HP
What is meant by shadowed guest page ? (Does it refer to : the guest PT
pages that have a corresponding shadow PT page)
I has been mentioned that: "The same page may already be mapped by the
guest in multiple locations. So, we track writable mappings of every
guest page ".
I can't understand why do we have to keep track of these reverse
mappings ? And what are these reverse mappings ? (from HP -> GP or HP ->
GV or GP -> GV)
Let's consider the following scenario:
GVA1 -> GPA1 -> HPA1
GVA2 -> GPA1 -> HPA1
Also, let GPA1 be part of a guest PT page.
i) The guest modifies a PTE in GPA1 by doing "mov GVA2"
ii) The host traps this as the page HPA1 is write-protected, and does
the corresponding modification to the guest PT page and its
corresponding shadow PT page.
(where do we need to use a reverse mapping)
I would be glad if you can point out where I am making the mistake.
--
Thanks & Regards,
Sukanto Ghosh
NB: GVA = guest virtual address GPA = guest physical address
HPA = host physical address
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