Date: Sat, 4 Jul 2015 10:12:40 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Denys Vlasenko <vda.linux@googlemail.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
        Rik van Riel <riel@redhat.com>, Oleg Nesterov <oleg@redhat.com>,
        Kees Cook <keescook@chromium.org>, Brian Gerst <brgerst@gmail.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v4 14/17] x86/asm/entry/64: Migrate error and interrupt
 exit work to C
Message-ID: <20150704081240.GA13132@gmail.com>
References: <cover.1435602481.git.luto@kernel.org>
 <1a5858d079609a3e293123c9ee45de433a4e9c44.1435602481.git.luto@kernel.org>
 <20150702120932.GH4001@pd.tnic>
 <CALCETrUhoxySrDCB0+qsGP3qRzkVML7Kp7-PgfcJdg0xzri6MQ@mail.gmail.com>
 <CAK1hOcPBK93Tx8XSUH7UyTQuWfwmu6o_wjK-RjH4=p5hxzf9_A@mail.gmail.com>
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* Andy Lutomirski <luto@amacapital.net> wrote:

> >> I'm torn on this one.  In principle, you're right, or we could have a macro 
> >> CALL_ENTER_FROM_USER_MODE that does nothing if context tracking is off.  
> >> OTOH, that's also kind of messy.
> >
> > busybox has IF() macros:
> >
> > IF_CONTEXT_TRACKING(call enter_from_user_mode)
> >
> > Unlike #if, this needs one line, not three.
> 
> I predict all of these call sites will get moved to C before 4.3.  If not, then 
> I'd be glad to clean this part up.

Ok, let's see how it works out.

I think in the initial phase we should be conservative and should attempt to 
introduce as few unrelated changes as possible, and get the conversion done. The 
current x86 entry code is a reasonable base to start with.

Once most of the 'mechanic' conversion is done we can do all the other changes.

The conversion itself is risky enough as-is, we want to offload as much of any 
other risk to after the conversion is done.

Thanks,

	Ingo
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