From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: [PATCH 06/12] xen: mark grant mapped pages as
 foreign
Date: Fri, 9 Jan 2015 16:19:36 +0000
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To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>, xen-devel@lists.xenproject.org, Jenny Herbert <jenny.herbert@citrix.com>, Jenny Herbert <jennifer.herbert@citrix.com>, David Vrabel <david.vrabel@citrix.com>
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On Fri, 2015-01-09 at 16:03 +0000, Stefano Stabellini wrote:
> On Tue, 6 Jan 2015, David Vrabel wrote:
> > From: Jenny Herbert <jennifer.herbert@citrix.com>
> > 
> > Use the "foreign" page flag to mark pages that have a grant map.  Use
> > page->private to store information of the grant (the granting domain
> > and the grant reference).
> > 
> > Signed-off-by: Jenny Herbert <jenny.herbert@citrix.com>
> > Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> > ---
> >  arch/x86/xen/p2m.c        |   50 ++++++++++++++++++++++++++++++++++++++-------
> >  include/xen/grant_table.h |   13 ++++++++++++
> >  2 files changed, 56 insertions(+), 7 deletions(-)
> > 
> > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> > index 0d70814..22624a3 100644
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -648,6 +648,43 @@ bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
> >  	return true;
> >  }
> >  
> > +static int
> > +init_page_grant_ref(struct page *p, domid_t domid, grant_ref_t grantref)
> > +{
> > +#ifdef CONFIG_X86_64
> > +	uint64_t gref;
> > +	uint64_t* gref_p = &gref;
> > +#else
> > +	uint64_t* gref_p = kmalloc(sizeof(uint64_t), GFP_KERNEL);
> > +	if (!gref)
> > +		return -ENOMEM;
> > +	uint64_t* gref = gref_p;
> > +#endif
> > +
> > +	*gref_p = ((uint64_t) grantref << 32) | domid;
> > +	p->private = gref;
> > +
> > +	WARN_ON(PagePrivate(p));
> > +	WARN_ON(PageForeign(p));
> > +	SetPagePrivate(p);
> > +	SetPageForeign(p);
> > +	return 0;
> > +}
> > +
> > +static void
> > +clear_page_grant_ref(struct page *p)
> > +{
> > +	WARN_ON(!PagePrivate(p));
> > +	WARN_ON(!PageForeign(p));
> > +
> > +#ifndef CONFIG_X86_64
> > +	kfree(p->private);
> > +#endif
> > +	p->private = 0;
> > +	ClearPagePrivate(p);
> > +	ClearPageForeign(p);
> > +}
> 
> Given that get_page_grant_ref is used by netback, these functions need
> to be made arch-independent, moved to an arch-independent code location
> and called appropriately.

... or stubbed out for arches which don't need this (which might include
arm*?).