On Thu, Mar 16, 2017 at 04:02:07PM +0530, Aneesh Kumar K.V wrote: > Max value supported by hardware is 51 bits address. Radix page table define > a slot of 57 bits for future expansion. We restrict the value supported in > linux kernel 51 bits, so that we can use the bits between 57-51 for storing > hash linux page table bits. This is done in the next patch. > > This will free up the software page table bits to be used for features > that are needed for both hash and radix. The current hash linux page table > format doesn't have any free software bits. Moving hash linux page table > specific bits to top of RPN field free up the software bits for other purpose. > > Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.vnet.ibm.com> > ---
There are a couple of comment typos below, but for the actual code change: Reviewed-by: Paul Mackerras <pau...@ozlabs.org> > arch/powerpc/include/asm/book3s/64/pgtable.h | 24 ++++++++++++++++++++++-- > 1 file changed, 22 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 96566df547a8..c470dcc815d5 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -38,6 +38,25 @@ > #define _RPAGE_RSV4 0x0200000000000000UL > #define _RPAGE_RPN0 0x01000 > #define _RPAGE_RPN1 0x02000 > +/* Max physicall address bit as per radix table */ physical not physicall > +#define _RPAGE_PA_MAX 57 > +/* > + * Max physical address bit we will use for now. > + * > + * This is mostly a hardware limitation and for now Power9 has > + * a 51 bit limit. > + * > + * This is different from the number of physical bit required to address > + * the last byte of memory. That is defined by MAX_PHYSMEM_BITS. > + * MAX_PHYSMEM_BITS is a linux limitation imposed by the maximum > + * number of sections we can support (SECTIONS_SHIFT). > + * > + * This is different from Radix page table limitation above and > + * should always be less than that. The limit is done such that > + * we can overload the bits between _RPAGE_PA_MAX and _PAGE_PA_MAX > + * for hash linux page table specific bits. > + */ > +#define _PAGE_PA_MAX 51 > > #define _PAGE_SOFT_DIRTY _RPAGE_SW3 /* software: software dirty tracking > */ > #define _PAGE_SPECIAL _RPAGE_SW2 /* software: special page */ > @@ -51,10 +70,11 @@ > */ > #define _PAGE_NO_CACHE _PAGE_TOLERANT > /* > - * We support 57 bit real address in pte. Clear everything above 57, and > + * We support _RPAGE_PA_MAX bit real address in pte. On the linux side > + * we are limited by _PAGE_PA_MAX. Clear everything above _PAGE_PA_MAX > * every thing below PAGE_SHIFT; You lost an "and" in that last sentence. > */ > -#define PTE_RPN_MASK (((1UL << 57) - 1) & (PAGE_MASK)) > +#define PTE_RPN_MASK (((1UL << _PAGE_PA_MAX) - 1) & (PAGE_MASK)) > /* > * set of bits not changed in pmd_modify. Even though we have hash specific > bits > * in here, on radix we expect them to be zero. > -- > 2.7.4 Paul.
