[PATCH 1/6] powerpc: Free up four 64K PTE bits in 4K backed HPTE pages

[Ram Pai]

On Thu, Jul 27, 2017 at 07:29:32AM +0530, Aneesh Kumar K.V wrote:
> 
> 
> On 07/26/2017 09:36 PM, Ram Pai wrote:
> >On Wed, Jul 26, 2017 at 04:05:48PM +0530, Aneesh Kumar K.V wrote:
> >>Ram Pai <linuxram at us.ibm.com> writes:
> >>
> 
> >>>diff --git a/arch/powerpc/include/asm/book3s/64/hash-64k.h b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> >>>index 9732837..62e580c 100644
> >>>--- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
> >>>+++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> >>>@@ -12,18 +12,14 @@
> >>>   */
> >>>  #define H_PAGE_COMBO	_RPAGE_RPN0 /* this is a combo 4k page */
> >>>  #define H_PAGE_4K_PFN	_RPAGE_RPN1 /* PFN is for a single 4k page */
> >>>+#define H_PAGE_BUSY	_RPAGE_RPN42     /* software: PTE & hash are busy */
> >>
> >>
> >>Why are we moving H_PAGE_BUSY. Right now 4k and 64k linux page table
> >>format looks similar.
> >
> >The goal is to clear off all the _RPAGE_RSV* bits so that they can be
> >used for protection keys.  the aim is to keep the protection-bits in the
> >_RPAGE_RSV* bits, so that they will work as-is whenever radix MMU enables
> >protection keys.
> >
> >Yes this makes the PTE format differ from 4k PTE. Hopefully it is a
> >small inconvenience. The PTE format for 4K is anyway not exactly the
> >same compared to 64K PTE format. For example, higher RPN bits are
> >used on 4K but not on 64k. lower RPN bits are used on 64k but not
> >on 4k.
> I was wondering why in this patch ? You do in the next patch

True. because in this patch, we have not yet freed up bit
_RPAGE_RPN44. _RPAGE_RPN44 bit is still used by H_PAGE_F_GIX for 64K
backed HPTEs.  Hence I have temporarily parked H_PAGE_BUSY at
_RPAGE_RPN42.

I could leave H_PAGE_BUSY at bit _RPAGE_RSV1  and move it to 
_RPAGE_RPN44 in the next patch. But by doing so, i would have not
truely released bit _RPAGE_RSV1 for 4K backed hptes; as claimed in the title
of this patch....  

> 
> --- a/arch/powerpc/include/asm/book3s/64/hash-64k.h
> +++ b/arch/powerpc/include/asm/book3s/64/hash-64k.h
> @@ -12,7 +12,7 @@
>   */
>  #define H_PAGE_COMBO	_RPAGE_RPN0 /* this is a combo 4k page */
>  #define H_PAGE_4K_PFN	_RPAGE_RPN1 /* PFN is for a single 4k page */
> -#define H_PAGE_BUSY	_RPAGE_RPN42     /* software: PTE & hash are busy */
> +#define H_PAGE_BUSY	_RPAGE_RPN44     /* software: PTE & hash are busy */
> 
...
-- 
Ram Pai