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Subject: Re: [PATCH 10/15] static_call: Add basic static call infrastructure
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <CAKv+Gu-rsZ2UsyEHbsZcSv9VVnFBqG70q+vk6thgMGFBi+vLSA@mail.gmail.com>
Date:   Fri, 7 Jun 2019 09:33:27 -0700
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Nadav Amit <namit@vmware.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
        David Laight <David.Laight@aculab.com>,
        Borislav Petkov <bp@alien8.de>,
        Julia Cartwright <julia@ni.com>, Jessica Yu <jeyu@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Edward Cree <ecree@solarflare.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
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References: <20190605130753.327195108@infradead.org> <20190605131945.125037517@infradead.org> <DD54886F-77C6-4230-A711-BF10DD44C52C@vmware.com> <20190607082851.GV3419@hirez.programming.kicks-ass.net> <CAKv+Gu-rsZ2UsyEHbsZcSv9VVnFBqG70q+vk6thgMGFBi+vLSA@mail.gmail.com>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Sender: linux-kernel-owner@vger.kernel.org
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> On Jun 7, 2019, at 1:49 AM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wro=
te:
>=20
>> On Fri, 7 Jun 2019 at 10:29, Peter Zijlstra <peterz@infradead.org> wrote:=

>>=20
>> On Thu, Jun 06, 2019 at 10:44:23PM +0000, Nadav Amit wrote:
>>>> + * Usage example:
>>>> + *
>>>> + *   # Start with the following functions (with identical prototypes):=

>>>> + *   int func_a(int arg1, int arg2);
>>>> + *   int func_b(int arg1, int arg2);
>>>> + *
>>>> + *   # Define a 'my_key' reference, associated with func_a() by defaul=
t
>>>> + *   DEFINE_STATIC_CALL(my_key, func_a);
>>>> + *
>>>> + *   # Call func_a()
>>>> + *   static_call(my_key, arg1, arg2);
>>>> + *
>>>> + *   # Update 'my_key' to point to func_b()
>>>> + *   static_call_update(my_key, func_b);
>>>> + *
>>>> + *   # Call func_b()
>>>> + *   static_call(my_key, arg1, arg2);
>>>=20
>>> I think that this calling interface is not very intuitive.
>>=20
>> Yeah, it is somewhat unfortunate..
>>=20
>=20
> Another thing I brought up at the time is that it would be useful to
> have the ability to 'reset' a static call to its default target. E.g.,
> for crypto modules that implement an accelerated version of a library
> interface, removing the module should revert those call sites back to
> the original target, without putting a disproportionate burden on the
> module itself to implement the logic to support this.

I was thinking this could be a layer on top.  We could have a way to registe=
r a static call with the module core so that, when a GPL module with an appr=
opriate symbol is loaded, the static call gets replaced.

KVM could use this too.  Or we could just require KVM to be built in some da=
y.