linux-kernel - Re: [RFC PATCH] Unexport do_machine_check() and machine_check

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Message-ID: <20160314180836.GJ15800@pd.tnic>
Date:	Mon, 14 Mar 2016 19:08:36 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Unexport do_machine_check() and machine_check_poll()

On Mon, Mar 14, 2016 at 09:55:17AM -0700, Luck, Tony wrote:
> It doesn't seem like a very natural fit ... the three routines
> take very different arguments which you bundle into a "void *".

Yeah, that was the quick'n'dirty approach.

> I'm also not sure what we gain. Now we have one, complicated,
> exported function that still lets modules do all the things
> they could do with the three separate functions.  Is there some
> benefit to having fewer exports?

So the small benefit is that our ABI has a single function instead of
two.

> What am I missing?

Yeah, you're right the patch is probably not the right thing to do.

But the sentiment is: I want to unexport do_machine_check() and
machine_check_poll() and not let external modules call into them
directly. Why, you ask? Because they have no business doing that. Those
two are MCA, more-or-less, internal functionality and it probably is ok
if mce-inject or kvm/vmx use them but the export is IMO too wide. Think
out-of-tree modules and whatnot here.

So I guess exporting even mce_call() is wrong - I'd like to not export
anything to users and allow only the existing two mce-inject and kvm/vmx
call them.

But the original reason why I started looking at those is that during a
backport to SLE11, I had a kABI issue due to machine_check_poll() and I
started questioning why is that function even exported? And it shouldn't
be - internal kernel users should be able to get that functionality in
a different way, without the wide export. I probably should think a bit
more about how.

I hope I'm making a bit more sense now...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.