[RFC PATCH 0/9] powerpc/mm: Restructure Linux PTE on Book3S/64 to radix format

[Paul Mackerras]

On Sun, Feb 21, 2016 at 01:11:17PM +0530, Aneesh Kumar K.V wrote:
> "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com> writes:
> 
> > Paul Mackerras <paulus at samba.org> writes:
> >
> >> This patch series modifies the Linux PTE format used on 64-bit Book3S
> >> processors (i.e. POWER server processors) to make the bits line up
> >> with the PTE format used in the radix trees defined in PowerISA v3.0.
> >> This will reduce the amount of further change required to make a
> >> kernel that can run with either a radix MMU or a hashed page table
> >> (HPT) MMU.
> >>
> >> This also changes the upper levels of the tree to use real addresses
> >> rather than kernel virtual addresses - that is, we no longer have the
> >> 0xc000... at the top of each PGD/PUD/PMD entry.  I made this change
> >> for all 64-bit machines, both embedded and server.
> >>
> >> The patch series is against v4.5-rc4 plus Aneesh's "powerpc/mm/hash:
> >> Clear the invalid slot information correctly" patch.
> >>
> >> I have compiled this for all the defconfigs in the tree, without
> >> error.  I have tested this, with the fixes branch of the powerpc tree
> >> merged in, both running bare-metal on a POWER8 and in a KVM guest on
> >> that POWER8 system.  In the guest I tested both 4k and 64k configs,
> >> with THP enabled; in the host I tested with 64k page size and THP
> >> enabled.  All these tests ran fine, including running a KVM guest on
> >> the bare-metal system.  So far I have done kernel compiles in a loop
> >> as the test, but I plan to run LTP and possibly some other tests.
> >>
> >> Comments welcome.
> >
> > I was expecting some complex changes in asm and other part of the code. That
> > is one of the reason I was holding of a series like this till I get the
> > radix merged. I should have really tried the radix/hash linux page table 
> > consolidation to see the impact.
> 
> One of the details that i hit last time with _PAGE_PTE was the usage of
> @h symbol in asm code. I did a quick look and I guess we are ok. But it
> will be good to double check. pmdp_splitting_flush (which got removed)
> had usages like %4 at h etc

I have done some pretty thorough grepping in arch/powerpc.  There is
no assembly code left that manipulates Linux PTEs (on 64-bit Book 3S,
that is), because you converted it all to C code. :)  There are a
couple of bits of inline asm, but the only bit that is used as an
immediate value is _PAGE_BUSY, which goes from 0x800 to 0x200, and
could actually stay at 0x800 in fact.

Paul.