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

From: Borislav Petkov
Date: Mon Nov 17 2014 - 13:50:50 EST

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.


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