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Date: Fri, 7 Jul 2017 14:48:44 -0400
From: Jerome Glisse <jglisse@...hat.com>
To: Igor Stoppa <igor.stoppa@...wei.com>
Cc: keescook@...omium.org, mhocko@...nel.org, jmorris@...ei.org,
	labbott@...hat.com, hch@...radead.org,
	penguin-kernel@...ove.SAKURA.ne.jp, paul@...l-moore.com,
	sds@...ho.nsa.gov, casey@...aufler-ca.com,
	linux-security-module@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 1/3] Protectable memory support

On Fri, Jul 07, 2017 at 11:42:09AM +0300, Igor Stoppa wrote:
> On 06/07/17 19:27, Jerome Glisse wrote:
> > On Wed, Jul 05, 2017 at 04:46:26PM +0300, Igor Stoppa wrote:

[...]

> > Yet another way is to use some of the free struct page fields ie
> > when a page is allocated for vmalloc i think most of struct page
> > fields are unuse (mapping, index, lru, ...). It would be better
> > to use those rather than adding a page flag.
> 
> Like introducing an unnamed union? Some sort of vmalloc_page_subtype?
> If that is what you are proposing, I agree that it would work in a
> similar fashion as what I have now, but without introducing the overhead
> of the extra page flag.

No need to introduce unamed union or anything. Just use one of the
existing field for install you can make page->mapping point to the
pmalloc pool structure. Or you can store a unique key value.

I believe there is enough unuse field that for vmalloc pages that
you should find one you can use. Just add some documentation in
mm_types.h so people are aware of alternate use for the field you
are using.

Jérôme

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