[tip:x86/fpu] x86/mpx: Add temporary variable to reduce masking

tip-bot for Dave Hansen
2015-06-09T12:35:23Z

Commit-ID: a1149fc83a1f97612e72ec24a0bdbabff7b85e77
Gitweb: http://git.kernel.org/tip/a1149fc83a1f97612e72ec24a0bdbabff7b85e77
Author: Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Sun, 7 Jun 2015 11:37:04 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 9 Jun 2015 12:24:33 +0200

x86/mpx: Add temporary variable to reduce masking

When we allocate a bounds table, we call mmap(), then add a
"valid" bit to the value before storing it in to the bounds
directory.

If we fail along the way, we go and mask that valid bit
_back_ out. That seems a little silly, and this makes it
much more clear when we have a plain address versus an
actual table _entry_.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150607183704.3D69D5F4@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/mm/mpx.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index c17fd27..4f7fb7c 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -429,6 +429,7 @@ static int allocate_bt(long __user *bd_entry)
unsigned long expected_old_val = 0;
unsigned long actual_old_val = 0;
unsigned long bt_addr;
+ unsigned long bd_new_entry;
int ret = 0;

/*
@@ -441,7 +442,7 @@ static int allocate_bt(long __user *bd_entry)
/*
* Set the valid flag (kinda like _PAGE_PRESENT in a pte)
*/
- bt_addr = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
+ bd_new_entry = bt_addr | MPX_BD_ENTRY_VALID_FLAG;

/*
* Go poke the address of the new bounds table in to the
@@ -455,7 +456,7 @@ static int allocate_bt(long __user *bd_entry)
* of the MPX code that have to pagefault_disable().
*/
ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
- expected_old_val, bt_addr);
+ expected_old_val, bd_new_entry);
if (ret)
goto out_unmap;

@@ -486,7 +487,7 @@ static int allocate_bt(long __user *bd_entry)
trace_mpx_new_bounds_table(bt_addr);
return 0;
out_unmap:
- vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);
+ vm_munmap(bt_addr, MPX_BT_SIZE_BYTES);
return ret;
}