[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>

arch/powerpc/Kconfig

@@ -603,6 +603,15 @@ config NODES_SPAN_OTHER_NODES
 	def_bool y
 	depends on NEED_MULTIPLE_NODES
 
+config PPC_64K_PAGES
+	bool "64k page size"
+	help
+	  This option changes the kernel logical page size to 64k. On machines
+          without processor support for 64k pages, the kernel will simulate
+          them by loading each individual 4k page on demand transparently,
+          while on hardware with such support, it will be used to map
+          normal application pages.
+
 config SCHED_SMT
 	bool "SMT (Hyperthreading) scheduler support"
 	depends on PPC64 && SMP

arch/powerpc/kernel/asm-offsets.c

@@ -125,6 +125,9 @@ int main(void)
 	DEFINE(PACASLBCACHE, offsetof(struct paca_struct, slb_cache));
 	DEFINE(PACASLBCACHEPTR, offsetof(struct paca_struct, slb_cache_ptr));
 	DEFINE(PACACONTEXTID, offsetof(struct paca_struct, context.id));
+#ifdef CONFIG_PPC_64K_PAGES
+	DEFINE(PACAPGDIR, offsetof(struct paca_struct, pgdir));
+#endif
 #ifdef CONFIG_HUGETLB_PAGE
 	DEFINE(PACALOWHTLBAREAS, offsetof(struct paca_struct, context.low_htlb_areas));
 	DEFINE(PACAHIGHHTLBAREAS, offsetof(struct paca_struct, context.high_htlb_areas));

arch/powerpc/kernel/cputable.c

@@ -240,7 +240,7 @@ struct cpu_spec	cpu_specs[] = {
 		.oprofile_model		= &op_model_power4,
 #endif
 	},
-	{	/* Power5 */
+	{	/* Power5 GR */
 		.pvr_mask		= 0xffff0000,
 		.pvr_value		= 0x003a0000,
 		.cpu_name		= "POWER5 (gr)",
@@ -255,7 +255,7 @@ struct cpu_spec	cpu_specs[] = {
 		.oprofile_model		= &op_model_power4,
 #endif
 	},
-	{	/* Power5 */
+	{	/* Power5 GS */
 		.pvr_mask		= 0xffff0000,
 		.pvr_value		= 0x003b0000,
 		.cpu_name		= "POWER5 (gs)",