[PATCH V2] powerpc/mm: Update mm context addr limit correctly.

[Aneesh Kumar K.V]

We added the addr < TASK_SIZE check to avoid updating addr_limit unnecessarily and
also to avoid calling slice_flush_segments on all the cpus. This had the side
effect of having different behaviour when using an addr value above TASK_SIZE
before updating addr_limit and after updating addr_limit as show by below
output:

requesting with hint 0x0
Addr returned 0x7fff893a0000
requesting with hint 0xffffffffffffffff
Addr returned 0x7fff891b0000                  <===== 1st return
requesting with hint 0x1000000000000
Addr returned 0x1000000000000
requesting with hint 0xffffffffffffffff
Addr returned 0x1ffff89410000                <==== second return

After fix:
requesting with hint 0x0
Addr returned 0x7fff8bc00000
requesting with hint 0xffffffffffffffff
Addr returned 0x1ffff8bc80000                <==== 1st return
requesting with hint 0x1000000000000
Addr returned 0x1000000000000
requesting with hint 0xffffffffffffffff
Addr returned 0x1ffff8bc60000                <==== second return

This also bring the ABI in-line with what is proposed on x86. ie, to use
a hint addr above 128TB up to and including (2^64)-1 as an indication to search
the full address space.

Fixes: f4ea6dcb08ea2c (powerpc/mm: Enable mappings above 128TB)
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
---

Changes from V1:
* Update with correct Fixes: sha1
* Also add information about how hint addr is used 

 arch/powerpc/mm/mmap.c  | 6 ++++--
 arch/powerpc/mm/slice.c | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
index b2111baa0da6..355b6fe8a1e6 100644
--- a/arch/powerpc/mm/mmap.c
+++ b/arch/powerpc/mm/mmap.c
@@ -97,7 +97,8 @@ radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	struct vm_area_struct *vma;
 	struct vm_unmapped_area_info info;
 
-	if (unlikely(addr > mm->context.addr_limit && addr < TASK_SIZE))
+	if (unlikely(addr > mm->context.addr_limit &&
+		     mm->context.addr_limit != TASK_SIZE))
 		mm->context.addr_limit = TASK_SIZE;
 
 	if (len > mm->context.addr_limit - mmap_min_addr)
@@ -139,7 +140,8 @@ radix__arch_get_unmapped_area_topdown(struct file *filp,
 	unsigned long addr = addr0;
 	struct vm_unmapped_area_info info;
 
-	if (unlikely(addr > mm->context.addr_limit && addr < TASK_SIZE))
+	if (unlikely(addr > mm->context.addr_limit &&
+		     mm->context.addr_limit != TASK_SIZE))
 		mm->context.addr_limit = TASK_SIZE;
 
 	/* requested length too big for entire address space */
diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
index 251b6bae7023..2d2d9760d057 100644
--- a/arch/powerpc/mm/slice.c
+++ b/arch/powerpc/mm/slice.c
@@ -419,7 +419,8 @@ unsigned long slice_get_unmapped_area(unsigned long addr, unsigned long len,
 	/*
 	 * Check if we need to expland slice area.
 	 */
-	if (unlikely(addr > mm->context.addr_limit && addr < TASK_SIZE)) {
+	if (unlikely(addr > mm->context.addr_limit &&
+		     mm->context.addr_limit != TASK_SIZE)) {
 		mm->context.addr_limit = TASK_SIZE;
 		on_each_cpu(slice_flush_segments, mm, 1);
 	}
-- 
2.7.4