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

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Message-ID: <CALCETrXMe_rvKBcZpGhodXO1WY44WHSyZM8OKQG-AXm=X0kMrw@mail.gmail.com>
Date:	Wed, 21 May 2014 15:24:18 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
	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, May 21, 2014 at 3:18 PM, Luck, Tony <tony.luck@...el.com> wrote:
>>> That TIF_MCE_NOTIFY prevents the return to user mode, and we end up in mce_notify_process().
>>
>> Why is this necessary?
>
> The recovery path has to do more than just send a signal - it needs to walk processes and
> "mm"s to see which have mapped the physical address that the h/w told us has gone bad.

I still feel like I'm missing something.  If we interrupted user space
code, then the context we're in should be identical to the context
we'll get when we're about to return to userspace.

--Andy
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