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    SubjectRe: [PATCH][RFC] pte notifiers -- support for external page tables
    Shaohua Li wrote:
    > On Wed, 2007-09-05 at 22:32 +0300, Avi Kivity wrote:
    >> [resend due to bad alias expansion resulting in some recipients
    >> being bogus]
    >> Some hardware and software systems maintain page tables outside the normal
    >> Linux page tables, which reference userspace memory. This includes
    >> Infiniband, other RDMA-capable devices, and kvm (with a pending patch).
    >> Because these systems maintain external page tables (and external tlbs),
    >> Linux cannot demand page this memory and it must be locked. For kvm at
    >> least, this is a significant reduction in functionality.
    >> This sample patch adds a new mechanism, pte notifiers, that allows drivers
    >> to register an interest in a changes to ptes. Whenever Linux changes a
    >> pte, it will call a notifier to allow the driver to adjust the external
    >> page table and flush its tlb.
    >> Note that only one notifier is implemented, ->clear(), but others should be
    >> similar.
    >> pte notifiers are different from paravirt_ops: they extend the normal
    >> page tables rather than replace them; and they provide high-level
    >> information
    >> such as the vma and the virtual address for the driver to use.
    > Looks great. So for kvm, all guest pages will be vma mapped?
    > There are lock issues in kvm between kvm lock and page lock.

    Yes, locking will be a headache.

    > Will shadow page table be still stored in page->private? If yes, the
    > page->private must be cleaned before add_to_swap.

    page->private can be in use by filesystems, so we will need to move rmap
    somewhere else.

    Any sufficiently difficult bug is indistinguishable from a feature.

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      Last update: 2007-09-06 10:43    [W:0.021 / U:45.244 seconds]
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