Re: [PATCH 1/3] mmu_notifier: Add mmu_notifier_invalidate_range()

From: Jesse Barnes
Date: Fri Jul 25 2014 - 16:16:46 EST

On Thu, 24 Jul 2014 16:35:39 +0200
Joerg Roedel <joro@xxxxxxxxxx> wrote:

> From: Joerg Roedel <jroedel@xxxxxxx>
> This notifier closes an important gap with the current
> invalidate_range_start()/end() notifiers. The _start() part
> is called when all pages are still mapped while the _end()
> notifier is called when all pages are potentially unmapped
> and already freed.
> This does not allow to manage external (non-CPU) hardware
> TLBs with MMU-notifiers because there is no way to prevent
> that hardware will establish new TLB entries between the
> calls of these two functions. But this is a requirement to
> the subsytem that implements these existing notifiers.
> To allow managing external TLBs the MMU-notifiers need to
> catch the moment when pages are unmapped but not yet freed.
> This new notifier catches that moment and notifies the
> interested subsytem when pages that were unmapped are about
> to be freed. The new notifier will only be called between
> invalidate_range_start()/end().

So if we were actually sharing page tables, we should be able to make
start/end no-ops and just use this new callback, assuming we didn't
need to do any other serialization or debug stuff, right?

Seems like a good addition, and saves us a bunch of trouble...

Jesse Barnes, Intel Open Source Technology Center
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