linux-kernel - Re: [PATCH] Don't allow the stack to grow into hugetlb reserved regions

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Message-ID: <Pine.LNX.4.64.0701270904360.15686@blonde.wat.veritas.com>
Date:	Sat, 27 Jan 2007 09:08:58 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Ken Chen <kenchen@...gle.com>
cc:	Adam Litke <agl@...ibm.com>, Andrew Morton <akpm@...l.org>,
	William Irwin <wli@...omorphy.com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Don't allow the stack to grow into hugetlb reserved
 regions

On Fri, 26 Jan 2007, Ken Chen wrote:
> On 1/26/07, Hugh Dickins <hugh@...itas.com> wrote:
> > Less trivial (and I wonder whether you've come to this from an ia64
> > or a powerpc direction): I notice that ia64 has more stringent REGION
> > checks in its ia64_do_page_fault, before calling expand_stack or
> > expand_upwards.  So on that path, the usual path, I think your
> > new check in acct_stack_growth is unnecessary on ia64;
> 
> I think you are correct. This appears to affect powerpc only. On ia64,
> hugetlb lives in a completely different region and they can never step
> into normal stack address space. And for x86, there isn't a thing called
> "reserved address space" for hugetlb mapping.

Thanks, that's reassuring for the hugetlb case, and therefore Adam's
patch should not be delayed.  But it does leave open the question I
was raising in the text you've snipped: if ia64 needs those stringent
REGION checks in its ia64_do_page_fault path, don't we need to add
them some(messy)how in the get_user_pages find_extend_vma path?

Hugh
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