Re: [Xen-devel] pagetable RO

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.10.13 at 08:30, åæ<zhangzhi2022@xxxxxxxxxxx> wrote:
>       Say, the sub-op: MMU_NORMAL_PT_UPDATE,
> if the page that ptr of struct mmu_update points to is PGT_l2_page_table, 
> then
> the address part of val of struct mmu_update points
> to a page, which is PGT_l1_page_table.
> However, I couldn't find the protections for this PGT_l1_page_table
> page in the do_mmu_update, is it already set as read-only
> before launching MMU_UPDATE hypercall?

Of course - a page can't be PGT_l1_page_table when there still is
some writable mapping around. So for an L2 entry update it is
sufficient to verify that all contained L1 entries point to R/O
pages (and transition them to PGT_l1_page_table if they aren't
already).

Jan

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