Messages in this thread | | | Date | Thu, 06 Sep 2007 11:38:20 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH][RFC] pte notifiers -- support for external page tables |
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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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