linux-kernel - Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace

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Message-ID: <CALCETrW75rES4=c1AYFXO0pobTZVjb6gYzpgWb0f9jAjYYduPQ@mail.gmail.com>
Date:	Mon, 17 Nov 2014 12:05:59 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [RFC PATCH] x86, entry: Switch stacks on a paranoid entry from userspace

On Mon, Nov 17, 2014 at 12:03 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Nov 17, 2014 at 11:57:22AM -0800, Andy Lutomirski wrote:
>> Would it be worth making a decision on task_work_add vs. stack
>> switching first?
>
> Probably a prudent thing to do in order to save unnecessary cycles :-)
>
>> Stack switching pros: all this lockless allocation stuff is completely
>> unnecessary, and it's plausible that the stack switching code will be
>> added anyway.
>
> Yes.
>
> However, I'd like to be very sure this thing doesn't introduce any
> regressions to the MCA code. So even if Tony's testing passes, I'd like
> to be very conservative here and stress it more than usual. Because once
> this thing hits upstream and stuff starts breaking, it'll be a serious
> PITA reverting it.
>
> I hope you can understand my concerns.

I agree completely.

>
> Btw, which branch has your latest version - I'd like to take a look at
> it in detail.

https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/paranoid

I'm not quite ready to send v3.  I want to do two things first:

1. Consider disabling the stack switch for double_fault.

2. Clean up the macros.  I'll validate this by ensuring that the
generated code is identical to the current version.

IOW, I don't expect the asm for machine_check to change.

--Andy
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