[CRIU] Re: [PATCH] Take into account stack guard page size in parse_smaps

[Cyrill Gorcunov]

On Tue, Jul 24, 2012 at 11:18:00AM +0400, Pavel Emelyanov wrote:
> >> This page is technically out of any mappings and reading pagemap for
> >> those is not ... safe. Is it?
> > 
> > Look, here is two problems actually in no taking this page into account
> > on dumping procedure
> > 
> >  - if it's not added into VMA size while being dumped we do shrink program
> >    stack at dumping procedure and once we support mulishot c/r we end up
> >    in situation where we might simply loose stack vma completely after
> >    some c/r session (simply because kernel accept "size" at mmap call
> >    but cuts off this page internally and report us this vma as "size-page")
> 
> NAK. We're talking about the guard page, which is added by kernel always.
> >  - reading pagemap should not be a problem since pagemap operates on page
> >    level rather than vma level, and on page level this guard area lacks
> >    "present" bit (the kernel actually might expand stack if needed though,
> >     see handle_pte_fault -> do_anonymous_page)
> 
> NAK again. pagemap works on pte level (how could it report swapout pages?).

By "page" I mean the PTE level. Anyway, you're right. Please pick up
http://openvz.org/pipermail/criu/2012-July/003777.html instead.

	Cyrill