linux-kernel - Can I use static keys from asm?

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Message-ID: <CALCETrWzSDe6SiU_nUK+vZcHKbWGbmujVdnQFDMFsG=1O-ofqA@mail.gmail.com>
Date:	Mon, 17 Aug 2015 18:34:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Can I use static keys from asm?

I have the following silly problem:

For kernels with context tracking compiled in, we need to call the
context tracking hooks if context tracking is enabled.

There are four interesting cases:

1. Context tracking disabled in config.  This is easy to handle.

2. Context tracking enabled in config but completely disabled at
runtime.  Distros do this.  I want to nop out the context tracking
hooks.  We have a static_key for this, but half the hooks are in asm.

3. Context tracking enabled in config but disabled on the current CPU.
I don't care all that much.

4. Context tracking enabled for real.  Performance will suck.  I want
to fix that, and I think my cleanups will make it a lot easier, but
we're not there yet.

To unsuck case 2, static keys in asm would help.  Can I do that?  It
would be even better if I could do that in 4.3.

FWIW, this might be unnecessary in the long run.  As more of this
spaghetti moves into C, the need for static keys in asm will be
reduced :)

--Andy
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