Re: [PATCH 00/23] Add KVM support for PPC64 (970) host

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2009-07-08 at 13:04 +0300, Avi Kivity wrote:
> 
> In this case how can hooking the hashes work?
> 
> kvm obtains pages by calling get_user_pages_fast() so you can have a 
> page in the shadow hash which is not present in the host hash.
> 
I'm not sure why we would have a problem with that actually. But again,
it depends how Alex does his stuff...

We -must- keep track that a given Linux PTE was hashed, we must not put
something into the hash without keeping that track or bad things will
happen such as potential duplicates etc...

We have fields in the PTE for that though I would have to understand
how Alex handles translated entries there.

If a guest entry is in the real hash, we thus must have some tracking
in the linux PTE that this guest entry is there to properly invalidate
it when the PTE is invalidated.

Now we could probably use the mmu_notifiers for that, but we have
existing mechanism to do that tracking and I think we might just
be able to re-use them, but of course, that needs to be looked at it
more details.

Cheers,
Ben.