Date: Fri, 21 Aug 2015 09:50:35 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Andy Lutomirski <luto@kernel.org>,
        X86 ML <x86@kernel.org>, Sasha Levin <sasha.levin@oracle.com>,
        Brian Gerst <brgerst@gmail.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH] x86/entry/64: Context-track syscalls before enabling
 interrupts
Message-ID: <20150821075035.GB9511@gmail.com>
References: <ad9154dd60f669e94e60d36d23c3267b2ac4c94d.1439924771.git.luto@kernel.org>
 <20150818221623.GA12858@lerouge>
 <CALCETrVQCi_RZqRSTy9bs0V+RB6cLHVfYq4Ouq_JLMoJePg1zA@mail.gmail.com>
 <20150818230235.GA13685@lerouge>
 <CALCETrVqA0JVxZeD+7vMD-9xmF8udXw5RO0fwQA2X45DSVqM0Q@mail.gmail.com>
 <20150819171007.GA21717@lerouge>
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> > I want to have a real hook to call that says "switch to IRQ context from 
> > CONTEXT_USER" or "switch to IRQ context from CONTEXT_KERNEL" (aka noop), but 
> > that doesn't currently exist.
> 
> You're not answering _why_ you want that.

So we'd have a comprehensive, 100% coverage, self-sufficient set of callbacks that 
track the kernel's current context state at the points where the context switches 
actually occur - not just something cobbled together heterogenously. The low level 
x86 asm code was rather messy in this area, better organization would be welcome, 
I don't think we can overdo it.

( I'm assuming here that it can all be done for zero or negative cost, and that
  the result will be correct and won't hurt existing users in any fashion. )

Thanks,

	Ingo
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