linux-kernel - Re: [PATCH 0/3] x86_64: Make int3 non-magical

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Message-ID: <CALCETrUe5q5fGXP=NG3mbz4AbmNdi519be1Z+-AeA6iOb9P3wg@mail.gmail.com>
Date:	Thu, 23 Jul 2015 15:39:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	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>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 0/3] x86_64: Make int3 non-magical

On Thu, Jul 23, 2015 at 3:37 PM, Andy Lutomirski <luto@...nel.org> wrote:
> int3 uses IST and the paranoid gsbase path.  Neither is necessary,
> although the IST stack may currently be necessary to avoid stack
> overruns.
>
> Clean up IRQ stacks, make them NMI safe, teach idtentry to use
> irqstacks if requested, and move int3 to the IRQ stack.
>
> This prepares us to return from int3 using RET.  While we could,
> in principle, return from an IST entry using RET, making that work
> seems likely to be much messier and more fragile than this approach.

Also, don't let the diffstat fool you.  If this works and if we can do
the same thing to do_debug, then we can do this:

https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_ist&id=1bc1f0ae8f1ea76486059a98cdbdfbdbc668aaf9

which makes it a big net win in complexity.

--Andy
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