linux-kernel - Re: [RFC] x86_64: A real proposal for iret-less return to kernel

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Message-ID: <CALCETrXO9EyWs5hykkAO2wU8udW0WE9AHfvjGog7s9ydPf4iEw@mail.gmail.com>
Date:	Wed, 21 May 2014 08:21:57 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On May 21, 2014 5:51 AM, "Jiri Kosina" <jkosina@...e.cz> wrote:
>
> On Tue, 20 May 2014, Andy Lutomirski wrote:
>
> > So the issue here is that we can have an NMI followed immediately by
> > an MCE.  The MCE code can call force_sig
>
> This is interesting by itself. force_sig() takes siglock spinlock. This
> really looks like a deadlock sitting there waiting to happen.

ISTM the do_machine_check code ought to consider any kill-worthy MCE
from kernel space to be non-recoverable, but I want to keep the scope
of these patches under control.

That being said, if an MCE that came from CPL0 never tried to return,
this would be simpler.  I don't know enough about the machine check
architecture to know whether that's a reasonable thing to do.

--Andy

>
> --
> Jiri Kosina
> SUSE Labs
>
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