From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [PATCH v2 10/21] arm64: KVM: Add patchable function selector
Date: Thu, 3 Dec 2015 08:18:43 +0000
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To: Andrew Jones <drjones@redhat.com>
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On Wed, 2 Dec 2015 16:34:56 -0600
Andrew Jones <drjones@redhat.com> wrote:

> On Fri, Nov 27, 2015 at 06:50:04PM +0000, Marc Zyngier wrote:
> > KVM so far relies on code patching, and is likely to use it more
> > in the future. The main issue is that our alternative system works
> > at the instruction level, while we'd like to have alternatives at
> > the function level.
> 
> How about setting static-keys at hyp init time?

That was an option I looked at. And while static keys would work to some
extent, they also have some nasty side effects:
- They create both a fast and a slow path. We don't want that - both
  path should be equally fast, or at least have as little overhead as
  possible
- We do need code patching for some assembly code, and using static
  keys on top creates a parallel mechanism that makes it hard to
  follow/debug/maintain.

You can view this alternative function call as a slightly different
kind of static keys - one that can give you the capability to handle
function calls instead of just jumping over code sequences. Both have
their own merits.

Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.