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

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Message-ID: <alpine.LNX.2.00.1405212323190.12047@pobox.suse.cz>
Date:	Wed, 21 May 2014 23:25:51 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Borislav Petkov <bp@...en8.de>
cc:	Andy Lutomirski <luto@...capital.net>,
	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 Wed, 21 May 2014, Borislav Petkov wrote:

> > 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.
> 
> MCA has a bit called RIPV which, if set, signals that RIP is valid and
> it is safe to return provided we've taken proper care of handling even
> non-correctable errors (memory poisoning, etc).

Yeah, but it tries to send SIGBUS from MCE context. And if MCE triggered 
at the time the CPU was already holding sighand->siglock for that 
particular task, it'll deadlock against itself.

-- 
Jiri Kosina
SUSE Labs
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