powerpc/44x: Support for 256KB PAGE_SIZE

This patch adds support for 256KB pages on ppc44x-based boards.

For simplification of implementation with 256KB pages we still assume
2-level paging. As a side effect this leads to wasting extra memory space
reserved for PTE tables: only 1/4 of pages allocated for PTEs are
actually used. But this may be an acceptable trade-off to achieve the
high performance we have with big PAGE_SIZEs in some applications (e.g.
RAID).

Also with 256KB PAGE_SIZE we increase THREAD_SIZE up to 32KB to minimize
the risk of stack overflows in the cases of on-stack arrays, which size
depends on the page size (e.g. multipage BIOs, NTFS, etc.).

With 256KB PAGE_SIZE we need to decrease the PKMAP_ORDER at least down
to 9, otherwise all high memory (2 ^ 10 * PAGE_SIZE == 256MB) we'll be
occupied by PKMAP addresses leaving no place for vmalloc. We do not
separate PKMAP_ORDER for 256K from 16K/64K PAGE_SIZE here; actually that
value of 10 in support for 16K/64K had been selected rather intuitively.
Thus now for all cases of PAGE_SIZE on ppc44x (including the default, 4KB,
one) we have 512 pages for PKMAP.

Because ELF standard supports only page sizes up to 64K, then you should
use binutils later than 2.17.50.0.3 with '-zmax-page-size' set to 256K
for building applications, which are to be run with the 256KB-page sized
kernel. If using the older binutils, then you should patch them like follows:

	--- binutils/bfd/elf32-ppc.c.orig
	+++ binutils/bfd/elf32-ppc.c

	-#define ELF_MAXPAGESIZE                0x10000
	+#define ELF_MAXPAGESIZE                0x40000

One more restriction we currently have with 256KB page sizes is inability
to use shmem safely, so, for now, the 256KB is available only if you turn
the CONFIG_SHMEM option off (another variant is to use BROKEN).
Though, if you need shmem with 256KB pages, you can always remove the !SHMEM
dependency in 'config PPC_256K_PAGES', and use the workaround available here:
 http://lkml.org/lkml/2008/12/19/20

Signed-off-by: Yuri Tikhonov <yur@emcraft.com>
Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>

7 files changed, 55 insertions, 9 deletions

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ccdd8de3c55..2d6d133c0ed 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -409,6 +409,18 @@ config PPC_HAS_HASH_64K
         depends on PPC64
         default n
 
+config STDBINUTILS
+        bool "Using standard binutils settings"
+        depends on 44x
+        default y
+        help
+          Turning this option off allows you to select 256KB PAGE_SIZE on 44x.
+          Note, that kernel will be able to run only those applications,
+          which had been compiled using binutils later than 2.17.50.0.3 with
+          '-zmax-page-size' set to 256K (the default is 64K). Or, if using
+          the older binutils, you can patch them with a trivial patch, which
+          changes the ELF_MAXPAGESIZE definition from 0x10000 to 0x40000.
+
 choice
         prompt "Page size"
         default PPC_4K_PAGES
@@ -444,6 +456,19 @@ config PPC_64K_PAGES
         bool "64k page size" if 44x || PPC_STD_MMU_64
         select PPC_HAS_HASH_64K if PPC_STD_MMU_64
 
+config PPC_256K_PAGES
+        bool "256k page size" if 44x
+        depends on !STDBINUTILS && (!SHMEM || BROKEN)
+        help
+          Make the page size 256k.
+
+          As the ELF standard only requires alignment to support page
+          sizes up to 64k, you will need to compile all of your user
+          space applications with a non-standard binutils settings
+          (see the STDBINUTILS description for details).
+
+          Say N unless you know what you are doing.
+
 endchoice
 
 config FORCE_MAX_ZONEORDER
@@ -456,6 +481,8 @@ config FORCE_MAX_ZONEORDER
         default "9" if PPC_STD_MMU_32 && PPC_16K_PAGES
         range 7 64 if PPC_STD_MMU_32 && PPC_64K_PAGES
         default "7" if PPC_STD_MMU_32 && PPC_64K_PAGES
+        range 5 64 if PPC_STD_MMU_32 && PPC_256K_PAGES
+        default "5" if PPC_STD_MMU_32 && PPC_256K_PAGES
         range 11 64
         default "11"
         help
diff --git a/arch/powerpc/include/asm/highmem.h b/arch/powerpc/include/asm/highmem.h
index 04e4a620952..a2907595067 100644
--- a/arch/powerpc/include/asm/highmem.h
+++ b/arch/powerpc/include/asm/highmem.h
@@ -39,15 +39,15 @@ extern pte_t *pkmap_page_table;
  * chunk of RAM.
  */
 /*
- * We use one full pte table with 4K pages. And with 16K/64K pages pte
- * table covers enough memory (32MB and 512MB resp.) that both FIXMAP
- * and PKMAP can be placed in single pte table. We use 1024 pages for
- * PKMAP in case of 16K/64K pages.
+ * We use one full pte table with 4K pages. And with 16K/64K/256K pages pte
+ * table covers enough memory (32MB/512MB/2GB resp.), so that both FIXMAP
+ * and PKMAP can be placed in a single pte table. We use 512 pages for PKMAP
+ * in case of 16K/64K/256K page sizes.
  */
 #ifdef CONFIG_PPC_4K_PAGES
 #define PKMAP_ORDER     PTE_SHIFT
 #else
-#define PKMAP_ORDER     10
+#define PKMAP_ORDER     9
 #endif
 #define LAST_PKMAP      (1 << PKMAP_ORDER)
 #ifndef CONFIG_PPC_4K_PAGES
diff --git a/arch/powerpc/include/asm/mmu-44x.h b/arch/powerpc/include/asm/mmu-44x.h
index 27cc6fdcd3b..3c86576bfef 100644
--- a/arch/powerpc/include/asm/mmu-44x.h
+++ b/arch/powerpc/include/asm/mmu-44x.h
@@ -83,6 +83,8 @@ typedef struct {
 #define PPC44x_TLBE_SIZE        PPC44x_TLB_16K
 #elif (PAGE_SHIFT == 16)
 #define PPC44x_TLBE_SIZE        PPC44x_TLB_64K
+#elif (PAGE_SHIFT == 18)
+#define PPC44x_TLBE_SIZE        PPC44x_TLB_256K
 #else
 #error "Unsupported PAGE_SIZE"
 #endif
diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
index 197d569f5bd..32cbf16f10e 100644
--- a/arch/powerpc/include/asm/page.h
+++ b/arch/powerpc/include/asm/page.h
@@ -19,12 +19,14 @@
 #include <asm/kdump.h>
 
 /*
- * On regular PPC32 page size is 4K (but we support 4K/16K/64K pages
+ * On regular PPC32 page size is 4K (but we support 4K/16K/64K/256K pages
  * on PPC44x). For PPC64 we support either 4K or 64K software
  * page size. When using 64K pages however, whether we are really supporting
  * 64K pages in HW or not is irrelevant to those definitions.
  */
-#if defined(CONFIG_PPC_64K_PAGES)
+#if defined(CONFIG_PPC_256K_PAGES)
+#define PAGE_SHIFT              18
+#elif defined(CONFIG_PPC_64K_PAGES)
 #define PAGE_SHIFT              16
 #elif defined(CONFIG_PPC_16K_PAGES)
 #define PAGE_SHIFT              14
diff --git a/arch/powerpc/include/asm/page_32.h b/arch/powerpc/include/asm/page_32.h
index 1458d950038..a0e3f6e6b4e 100644
--- a/arch/powerpc/include/asm/page_32.h
+++ b/arch/powerpc/include/asm/page_32.h
@@ -19,7 +19,11 @@
 #define PTE_FLAGS_OFFSET        0
 #endif
 
+#ifdef CONFIG_PPC_256K_PAGES
+#define PTE_SHIFT       (PAGE_SHIFT - PTE_T_LOG2 - 2)   /* 1/4 of a page */
+#else
 #define PTE_SHIFT       (PAGE_SHIFT - PTE_T_LOG2)       /* full page */
+#endif
 
 #ifndef __ASSEMBLY__
 /*
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 9665a26a253..e04286f92f6 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -12,8 +12,10 @@
 
 /* We have 8k stacks on ppc32 and 16k on ppc64 */
 
-#ifdef CONFIG_PPC64
+#if defined(CONFIG_PPC64)
 #define THREAD_SHIFT            14
+#elif defined(CONFIG_PPC_256K_PAGES)
+#define THREAD_SHIFT            15
 #else
 #define THREAD_SHIFT            13
 #endif
diff --git a/arch/powerpc/kernel/head_booke.h b/arch/powerpc/kernel/head_booke.h
index bec18078239..69a4489bc86 100644
--- a/arch/powerpc/kernel/head_booke.h
+++ b/arch/powerpc/kernel/head_booke.h
@@ -10,6 +10,15 @@
                 mtspr   SPRN_IVOR##vector_number,r26;   \
                 sync
 
+#if (THREAD_SHIFT < 15)
+#define ALLOC_STACK_FRAME(reg, val)                     \
+        addi reg,reg,val
+#else
+#define ALLOC_STACK_FRAME(reg, val)                     \
+        addis   reg,reg,val@ha;                         \
+        addi    reg,reg,val@l
+#endif
+
 #define NORMAL_EXCEPTION_PROLOG                                              \
         mtspr   SPRN_SPRG0,r10;         /* save two registers to work with */\
         mtspr   SPRN_SPRG1,r11;                                              \
@@ -20,7 +29,7 @@
         beq     1f;                                                          \
         mfspr   r1,SPRN_SPRG3;          /* if from user, start at top of   */\
         lwz     r1,THREAD_INFO-THREAD(r1); /* this thread's kernel stack   */\
-        addi    r1,r1,THREAD_SIZE;                                           \
+        ALLOC_STACK_FRAME(r1, THREAD_SIZE);                                  \
 1:      subi    r1,r1,INT_FRAME_SIZE;   /* Allocate an exception frame     */\
         mr      r11,r1;                                                      \
         stw     r10,_CCR(r11);          /* save various registers          */\