Messages in this thread | | | Date | Thu, 06 Sep 2007 16:18:23 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH][RFC] pte notifiers -- support for external page tables |
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[ugh, what happened to the cc-list?]
Andi Kleen wrote: > Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> writes: > >> 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. >> > > Sounds like a locking horror to me. To do anything with page tables > you need locks. Both for the kernel page tables and for your new tables. > > What happens when people add all > things of complicated operations in these notifiers? That will likely > happen and then everytime you change something in VM code they > will break. This has the potential to increase the cost of maintaining > VM code considerably, which would be a bad thing. > > This is quite different from paravirt ops because low level pvops > can typically run lockless by just doing some kind of hypercall directly. > But that won't work for maintaining your custom page tables. >
This is a real problem. I don't have a solution yet.
Obviously that needs to be addressed before something like this can go in; but as it's been done for the quadrics driver, presumably it is doable.
-- Any sufficiently difficult bug is indistinguishable from a feature.
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