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

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Message-ID: <20141117185030.GA25157@pd.tnic>
Date:	Mon, 17 Nov 2014 19:50:30 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	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 09:56:38PM +0000, Luck, Tony wrote:
> ...
> 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()

Well, I think we might do something with a lockless list as it is being
done in ghes.c.

It allocates entries from its own pool in the NMI handler and
llist_add's them to a list.

Then, in user context it does llist_del_all and then looks at each of
the elements at leisure and stress-free :-)

Pool alloc/free is NMI-safe too so we should be good. It looks pretty
clean, I'd give it a try.

> 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?

Start gets overwritten AFAICR.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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