[PATCH] ppc64: support 64k pages

Adds a new CONFIG_PPC_64K_PAGES which, when enabled, changes the kernel
base page size to 64K.  The resulting kernel still boots on any
hardware.  On current machines with 4K pages support only, the kernel
will maintain 16 "subpages" for each 64K page transparently.

Note that while real 64K capable HW has been tested, the current patch
will not enable it yet as such hardware is not released yet, and I'm
still verifying with the firmware architects the proper to get the
information from the newer hypervisors.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 14 insertions, 1 deletions

diff --git a/include/asm-ppc64/mmu_context.h b/include/asm-ppc64/mmu_context.h
index 820dd729b895..4f512e9fa6b8 100644
--- a/include/asm-ppc64/mmu_context.h
+++ b/include/asm-ppc64/mmu_context.h
@@ -16,8 +16,16 @@
  * 2 of the License, or (at your option) any later version.
  */
 
-static inline void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
+/*
+ * Getting into a kernel thread, there is no valid user segment, mark
+ * paca->pgdir NULL so that SLB miss on user addresses will fault
+ */
+static inline void enter_lazy_tlb(struct mm_struct *mm,
+                                  struct task_struct *tsk)
 {
+#ifdef CONFIG_PPC_64K_PAGES
+        get_paca()->pgdir = NULL;
+#endif /* CONFIG_PPC_64K_PAGES */
 }
 
 #define NO_CONTEXT      0
@@ -40,8 +48,13 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
                 cpu_set(smp_processor_id(), next->cpu_vm_mask);
 
         /* No need to flush userspace segments if the mm doesnt change */
+#ifdef CONFIG_PPC_64K_PAGES
+        if (prev == next && get_paca()->pgdir == next->pgd)
+                return;
+#else
         if (prev == next)
                 return;
+#endif /* CONFIG_PPC_64K_PAGES */
 
 #ifdef CONFIG_ALTIVEC
         if (cpu_has_feature(CPU_FTR_ALTIVEC))