powerpc: Use 64k pages without needing cache-inhibited large pages

Some POWER5+ machines can do 64k hardware pages for normal memory but
not for cache-inhibited pages.  This patch lets us use 64k hardware
pages for most user processes on such machines (assuming the kernel
has been configured with CONFIG_PPC_64K_PAGES=y).  User processes
start out using 64k pages and get switched to 4k pages if they use any
non-cacheable mappings.

With this, we use 64k pages for the vmalloc region and 4k pages for
the imalloc region.  If anything creates a non-cacheable mapping in
the vmalloc region, the vmalloc region will get switched to 4k pages.
I don't know of any driver other than the DRM that would do this,
though, and these machines don't have AGP.

When a region gets switched from 64k pages to 4k pages, we do not have
to clear out all the 64k HPTEs from the hash table immediately.  We
use the _PAGE_COMBO bit in the Linux PTE to indicate whether the page
was hashed in as a 64k page or a set of 4k pages.  If hash_page is
trying to insert a 4k page for a Linux PTE and it sees that it has
already been inserted as a 64k page, it first invalidates the 64k HPTE
before inserting the 4k HPTE.  The hash invalidation routines also use
the _PAGE_COMBO bit, to determine whether to look for a 64k HPTE or a
set of 4k HPTEs to remove.  With those two changes, we can tolerate a
mix of 4k and 64k HPTEs in the hash table, and they will all get
removed when the address space is torn down.

Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 2 insertions, 8 deletions

diff --git a/include/asm-powerpc/pgtable.h b/include/asm-powerpc/pgtable.h
index e9f1f4627e6b..260a0fabe97e 100644
--- a/include/asm-powerpc/pgtable.h
+++ b/include/asm-powerpc/pgtable.h
@@ -47,8 +47,8 @@ struct mm_struct;
 /*
  * Define the address range of the vmalloc VM area.
  */
-#define VMALLOC_START (0xD000000000000000ul)
-#define VMALLOC_SIZE  (0x80000000000UL)
+#define VMALLOC_START ASM_CONST(0xD000000000000000)
+#define VMALLOC_SIZE  ASM_CONST(0x80000000000)
 #define VMALLOC_END   (VMALLOC_START + VMALLOC_SIZE)
 
 /*
@@ -413,12 +413,6 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
                 flush_tlb_pending();
         }
         pte = __pte(pte_val(pte) & ~_PAGE_HPTEFLAGS);
-
-#ifdef CONFIG_PPC_64K_PAGES
-        if (mmu_virtual_psize != MMU_PAGE_64K)
-                pte = __pte(pte_val(pte) | _PAGE_COMBO);
-#endif /* CONFIG_PPC_64K_PAGES */
-
         *ptep = pte;
 }