linux-kernel - Re: [PATCH 1/3] x86/entry/64: Refactor IRQ stacks and make then NMI-safe

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Date:	Sat, 25 Jul 2015 06:16:56 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>, Willy Tarreau <w@....eu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/3] x86/entry/64: Refactor IRQ stacks and make then
 NMI-safe

On Fri, Jul 24, 2015 at 11:02:51AM -0700, Andy Lutomirski wrote:
> So really the only difference between this simple approach (which is
> more or less what we do now) and my fancy approach is that a kernel
> instruction breakpoint will cause do_debug to run on the initial stack
> instead of the IRQ stack.

Sounds ok to me. What would be the worst thing if we limited the #DB
stack? Some breakpoints will get ignored? In an endless stream of
breakpoints hammering? Doesn't sound like a valid use case to me, does
it?

> I'm still tempted to say we should use my overly paranoid atomic
> approach for now and optimize later,...

But why change it if the simple approach of incrementing irq_count first
is still fine? I think we want to KISS here exactly because apparently
complexity in that area is a serious PITA...

-- 
Regards/Gruss,
    Boris.

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