Re: [PATCH 2/4] mm: introduce mm_forbids_zeropage function

[Dominik Dingel <dingel@linux.vnet.ibm.com>]

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

> On Wed, 22 Oct 2014 13:09:28 +0200 Dominik Dingel <dingel@linux.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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