linux-kernel - Re: [PATCH] x86/entry/64: Context-track syscalls before enabling interrupts

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Message-ID: <20150821075035.GB9511@gmail.com>
Date:	Fri, 21 Aug 2015 09:50:35 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] x86/entry/64: Context-track syscalls before enabling
 interrupts

* Frederic Weisbecker <fweisbec@...il.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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