[PATCH v2 9/9] powerpc: Simplify and move arch_randomize_brk()

[Christophe Leroy]

arch_randomize_brk() is only needed for hash on book3s/64, for other
platforms the one provided by the default mmap layout is good enough.

Move it to hash_utils.c and use randomize_page() like the generic one.

And properly opt out the radix case instead of making an assumption
on mmu_highuser_ssize.

Also change to a 32M range like most other architectures instead of 8M.

Signed-off-by: Christophe Leroy <christophe.leroy at csgroup.eu>
---
v2: New
---
 arch/powerpc/kernel/process.c         | 40 ---------------------------
 arch/powerpc/mm/book3s64/hash_utils.c | 18 ++++++++++++
 include/linux/sizes.h                 |  2 ++
 3 files changed, 20 insertions(+), 40 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 406d7ee9e322..f1f2f17543d6 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2274,43 +2274,3 @@ unsigned long arch_align_stack(unsigned long sp)
 		sp -= get_random_int() & ~PAGE_MASK;
 	return sp & ~0xf;
 }
-
-static inline unsigned long brk_rnd(void)
-{
-        unsigned long rnd = 0;
-
-	/* 8MB for 32bit, 1GB for 64bit */
-	if (is_32bit_task())
-		rnd = (get_random_long() % (1UL<<(23-PAGE_SHIFT)));
-	else
-		rnd = (get_random_long() % (1UL<<(30-PAGE_SHIFT)));
-
-	return rnd << PAGE_SHIFT;
-}
-
-unsigned long arch_randomize_brk(struct mm_struct *mm)
-{
-	unsigned long base = mm->brk;
-	unsigned long ret;
-
-#ifdef CONFIG_PPC_BOOK3S_64
-	/*
-	 * If we are using 1TB segments and we are allowed to randomise
-	 * the heap, we can put it above 1TB so it is backed by a 1TB
-	 * segment. Otherwise the heap will be in the bottom 1TB
-	 * which always uses 256MB segments and this may result in a
-	 * performance penalty. We don't need to worry about radix. For
-	 * radix, mmu_highuser_ssize remains unchanged from 256MB.
-	 */
-	if (!is_32bit_task() && (mmu_highuser_ssize == MMU_SEGSIZE_1T))
-		base = max_t(unsigned long, mm->brk, 1UL << SID_SHIFT_1T);
-#endif
-
-	ret = PAGE_ALIGN(base + brk_rnd());
-
-	if (ret < mm->brk)
-		return mm->brk;
-
-	return ret;
-}
-
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index 1d09d4aeddbf..3521fad6a479 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -37,6 +37,7 @@
 #include <linux/cpu.h>
 #include <linux/pgtable.h>
 #include <linux/debugfs.h>
+#include <linux/random.h>
 
 #include <asm/interrupt.h>
 #include <asm/processor.h>
@@ -2072,3 +2073,20 @@ void __init print_system_hash_info(void)
 	if (htab_hash_mask)
 		pr_info("htab_hash_mask    = 0x%lx\n", htab_hash_mask);
 }
+
+unsigned long arch_randomize_brk(struct mm_struct *mm)
+{
+	/*
+	 * If we are using 1TB segments and we are allowed to randomise
+	 * the heap, we can put it above 1TB so it is backed by a 1TB
+	 * segment. Otherwise the heap will be in the bottom 1TB
+	 * which always uses 256MB segments and this may result in a
+	 * performance penalty.
+	 */
+	if (is_32bit_task())
+		return randomize_page(mm->brk, SZ_32M);
+	else if (!radix_enabled() && mmu_highuser_ssize == MMU_SEGSIZE_1T)
+		return randomize_page(max_t(unsigned long, mm->brk, SZ_1T), SZ_1G);
+	else
+		return randomize_page(mm->brk, SZ_1G);
+}
diff --git a/include/linux/sizes.h b/include/linux/sizes.h
index 1ac79bcee2bb..84aa448d8bb3 100644
--- a/include/linux/sizes.h
+++ b/include/linux/sizes.h
@@ -47,6 +47,8 @@
 #define SZ_8G				_AC(0x200000000, ULL)
 #define SZ_16G				_AC(0x400000000, ULL)
 #define SZ_32G				_AC(0x800000000, ULL)
+
+#define SZ_1T				_AC(0x10000000000, ULL)
 #define SZ_64T				_AC(0x400000000000, ULL)
 
 #endif /* __LINUX_SIZES_H__ */
-- 
2.33.1