Re: RFC: New API for PPC for vcpu mmu access

[Scott Wood <scottwood@freescale.com>]

On Fri, 11 Feb 2011 02:41:35 +0100
Alexander Graf <agraf@suse.de> wrote:

> >> Maybe we should go with Avi's proposal after all and simply keep the full soft-mmu synced between kernel and user space? That way we only need a setup call at first, no copying in between and simply update the user space version whenever something changes in the guest. We need to store the TLB's contents off somewhere anyways, so all we need is an additional in-kernel array with internal translation data, but that can be separate from the guest visible data, right?

Hmm, the idea is growing on me.

> So then everything we need to get all the functionality we need is a hint from kernel to user space that something changed and vice versa.
> 
> From kernel to user space is simple. We can just document that after every RUN, all fields can be modified.
> From user space to kernel, we could modify the entries directly and then pass in an ioctl that passes in a dirty bitmap to kernel space. KVM can then decide what to do with it. I guess the easiest implementation for now would be to ignore the bitmap and simply flush the shadow tlb.
> 
> That gives us the flush almost for free. All we need to do is set the tlb to all zeros (should be done by env init anyways) and pass in the "something changed" call. KVM can then decide to simply drop all of its shadow state or loop through every shadow entry and flush it individually. Maybe we should give a hint on the amount of flushes, so KVM can implement some threshold.

OK.  We'll also need a config ioctl to specify MMU type/size and the address
of the arrays.

> Also, please tell me you didn't implement the previous revisions already.

I didn't. :-)

-Scott