Re: [PATCH 03/17] perf, x86: Add copy_from_user_nmi_nochk for besteffort copy

[Jiri Olsa]

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
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