linux-kernel - Re: [PATCH 2/4] mm: introduce mm_forbids

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Message-ID: <20141022214552.0c954692@BR9TG4T3.de.ibm.com>
Date:	Wed, 22 Oct 2014 21:45:52 +0200
From:	Dominik Dingel <dingel@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Bob Liu <lliubbo@...il.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Gleb Natapov <gleb@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jianyu Zhan <nasa4836@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	kvm@...r.kernel.org, linux390@...ibm.com,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH 2/4] mm: introduce mm_forbids_zeropage function

On Wed, 22 Oct 2014 12:22:23 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 22 Oct 2014 13:09:28 +0200 Dominik Dingel <dingel@...ux.vnet.ibm.com> wrote:
> 
> > Add a new function stub to allow architectures to disable for
> > an mm_structthe backing of non-present, anonymous pages with
> > read-only empty zero pages.
> > 
> > ...
> >
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -56,6 +56,10 @@ extern int sysctl_legacy_va_layout;
> >  #define __pa_symbol(x)  __pa(RELOC_HIDE((unsigned long)(x), 0))
> >  #endif
> >  
> > +#ifndef mm_forbids_zeropage
> > +#define mm_forbids_zeropage(X)  (0)
> > +#endif
> 
> Can we document this please?  What it does, why it does it.  We should
> also specify precisely which arch header file is responsible for
> defining mm_forbids_zeropage.
> 

I will add a comment like:

/*
 * To prevent common memory management code establishing
 * a zero page mapping on a read fault.
 * This function should be implemented within <asm/pgtable.h>.
 * s390 does this to prevent multiplexing of hardware bits
 * related to the physical page in case of virtualization.
 */

Okay?


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