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Subject: Re: [PATCH v7 3/7] powerpc/mm: Introduce _PAGE_LARGE software pte bits
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Balbir Singh <bsingharora@gmail.com>, "Aneesh Kumar K.V"
 <aneesh.kumar@linux.vnet.ibm.com>, paulus@samba.org, mpe@ellerman.id.au
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Date: Wed, 30 Nov 2016 11:35:13 +1100
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On Wed, 2016-11-30 at 11:14 +1100, Balbir Singh wrote:
> > +#define _RPAGE_RSV1          0x1000000000000000UL
> > +#define _RPAGE_RSV2          0x0800000000000000UL
> > +#define _RPAGE_RSV3          0x0400000000000000UL
> > +#define _RPAGE_RSV4          0x0200000000000000UL
> > +
> 
> We use the top 4 bits and not the _SW bits?

Correct, welcome to the discussion we've been having the last 2 weeks
:-)

We use those bits because we are otherwise short on SW bits (we still
need _PAGE_DEVMAP etc...). We know P9 DD1 is supposed to ignore the
reserved bits so it's a good place holder.

Cheers,
Ben.