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Date: Wed, 25 Jul 2012 19:35:05 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: acme@redhat.com, a.p.zijlstra@chello.nl, mingo@elte.hu, paulus@samba.org,
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        benjamin.redelings@nescent.org
Subject: Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi_nochk for best
 effort copy
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On Wed, Jul 25, 2012 at 07:30:31PM +0200, Jiri Olsa wrote:
> On Wed, Jul 25, 2012 at 07:16:43PM +0200, Jiri Olsa wrote:
> > On Wed, Jul 25, 2012 at 06:11:53PM +0200, Frederic Weisbecker wrote:
> > > On Sun, Jul 22, 2012 at 02:14:26PM +0200, Jiri Olsa wrote:
> > > > Adding copy_from_user_nmi_nochk that provides the best effort
> > > > copy regardless the requesting size crossing the task boundary.
> > > > 
> > > > This is going to be useful for stack dump we need in post
> > > > DWARF CFI based unwind, where we have predefined size of
> > > > the user stack to dump, and we need to store the most of
> > > > the requested dump size, regardless this size is crossing
> > > > the task boundary.
> > > 
> > > What does that imply when we cross this limit? Are we still in the
> > > task stack?
> > 
> > We store all we could from 'stack pointer' to 'stack pointer' + dump size.
> > 
> > I discussed this with Oleg and we could probably find vma for the 'stack pointer'
> > and check for its size and narrow the dump - maybe more complex, but probably faster
> > in comparison with dumping pages we're not interested in.
> > 
> > thanks,
> > jirka
> 
> I can send this update later together with vdso
> and 'syscall regs storage' features ;)

Sure! As long as we are fine with the kernel ABI, the rest can be done
incrementally.