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

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Message-ID: <CALCETrW+3TQvZAQfo5HsiHDku8C125sn5dNffOGKOeCHjZZrbw@mail.gmail.com>
Date:	Fri, 14 Nov 2014 14:07:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Borislav Petkov <bp@...en8.de>, 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 Fri, Nov 14, 2014 at 1:56 PM, Luck, Tony <tony.luck@...el.com> wrote:
>>> Right, I can do it in the meantime and we can always experiment more
>>> later. Getting rid of _TIF_MCE_NOTIFY is a good thing already.
>>
>> Yep, it looks pretty simple - not tested yet, it builds though.
>
> It seems pretty solid under test so far.
>
> Can we make it pass the address/flag to mce_notify_process() too? So
> we can get rid of mce_save_info() and mce_find_info().
>
> We'd need to wrap mce_task_work inside a bigger structure with fields
> to have the address and flags - then use "container_of" inside mce_notify_process().
>
> But I think that means we need more than one of these structures ... we may not
> be done with one before a new machine check occurs. So we'd have to make an
> NMI-safe allocator to grab one for use inside do_machine_check()

I think that this is a considerable benefit of my code, aside from the
non-working-ness part.  :-/

--Andy

>
> -Tony
>
> General testing note - one thing I did see was that if inject 1000 errors at 0.3s interval from
> my ssh'd login ... the serial console keeps streaming messages for about 40 seconds
> after my test says it is all done. This might be a factor in the other tests I've been
> running against the stack-switching code (especially with extra debug) ... at some
> point __log_buf must get full - what happens then?



-- 
Andy Lutomirski
AMA Capital Management, LLC
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