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    SubjectRe: Xen MMU's requirement to pin pages RO and initial_memory_mapping.
    > > xen_alloc_pte_init and xen_alloc_pmd_init are the ones that mark the
    > > pagetable pages RO and pin them, calling make_lowmem_page_readonly and
    > > pin_pagetable_pfn.
    > >
    > > alloc_pte/pmd are called right before hooking them into the pagetable;
    > > unfortunately that means that they fail at marking the pagetable pages
    > > RO: make_lowmem_page_readonly uses lookup_address to find the pte
    > > corresponding to a page, however at this point the pagetable pages are
    > > not mapped yet (usually they are not hooked but when they are hooked, the
    > > upper level pagetable page is not hooked), so lookup_address fails.
    >
    > Right. We don't have to walk the hooked pagetable, I think. We are passed
    > in the PMD/PGD of the PFN and we could look at the content of that PFN.

    err, got that backwards. "passed in the PFN of the PMD/PGD".


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