[patch 5/6] powerpc: Add Strong Access Ordering

shaggy
2008-06-18T22:32:59Z

Allow an application to enable Strong Access Ordering on specific pages of
memory on Power 7 hardware. Currently, power has a weaker memory model than
x86. Implementing a stronger memory model allows an emulator to more
efficiently translate x86 code into power code, resulting in faster code
execution.

On Power 7 hardware, storing 0b1110 in the WIMG bits of the hpte enables
strong access ordering mode for the memory page. This patchset allows a
user to specify which pages are thus enabled by passing a new protection
bit through mmap() and mprotect(). I have tentatively defined this bit,
PROT_SAO, as 0x10.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
---

arch/powerpc/kernel/syscalls.c | 3 +++
include/asm-powerpc/mman.h | 28 ++++++++++++++++++++++++++++
2 files changed, 31 insertions(+)

Index: linux-2.6.26-rc5/arch/powerpc/kernel/syscalls.c
===================================================================
--- linux-2.6.26-rc5.orig/arch/powerpc/kernel/syscalls.c
+++ linux-2.6.26-rc5/arch/powerpc/kernel/syscalls.c
@@ -143,6 +143,9 @@ static inline unsigned long do_mmap2(uns
struct file * file = NULL;
unsigned long ret = -EINVAL;

+ if (!arch_validate_prot(prot))
+ goto out;
+
if (shift) {
if (off & ((1 << shift) - 1))
goto out;
Index: linux-2.6.26-rc5/include/asm-powerpc/mman.h
===================================================================
--- linux-2.6.26-rc5.orig/include/asm-powerpc/mman.h
+++ linux-2.6.26-rc5/include/asm-powerpc/mman.h
@@ -1,7 +1,9 @@
#ifndef _ASM_POWERPC_MMAN_H
#define _ASM_POWERPC_MMAN_H

+#include <asm/cputable.h>
#include <asm-generic/mman.h>
+#include <linux/mm.h>

/*
* This program is free software; you can redistribute it and/or
@@ -26,4 +28,30 @@
#define MAP_POPULATE 0x8000 /* populate (prefault) pagetables */
#define MAP_NONBLOCK 0x10000 /* do not block on IO */

+/*
+ * This file is included by linux/mman.h, so we can't use cacl_vm_prot_bits()
+ * here. How important is the optimization?
+ */
+static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot)
+{
+ return (prot & PROT_SAO) ? VM_SAO : 0;
+}
+#define arch_calc_vm_prot_bits(prot) arch_calc_vm_prot_bits(prot)
+
+static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
+{
+ return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : 0;
+}
+#define arch_vm_get_page_prot(vm_flags) arch_vm_get_page_prot(vm_flags)
+
+static inline int arch_validate_prot(unsigned long prot)
+{
+ if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_SAO))
+ return 0;
+ if ((prot & PROT_SAO) && !cpu_has_feature(CPU_FTR_SAO))
+ return 0;
+ return 1;
+}
+#define arch_validate_prot(prot) arch_validate_prot(prot)
+
#endif /* _ASM_POWERPC_MMAN_H */

--