diff options
| author | Andy Lutomirski <[email protected]> | 2015-10-05 17:48:20 -0700 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-10-09 09:41:12 +0200 |
| commit | c68ca6787bdd6d2df37cf950135aa11e71af358a (patch) | |
| tree | e4c1c92be7f20cd4dc4b74ed605d494bc4154afb | |
| parent | 33c52129f45e06d9ce23e1a3d50bf9fd6770748b (diff) | |
x86/entry: Micro-optimize compat fast syscall arg fetch
We're following a 32-bit pointer, and the uaccess code isn't
smart enough to figure out that the access_ok() check isn't
needed.
This saves about three cycles on a cache-hot fast syscall.
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/bdff034e2f23c5eb974c760cf494cb5bddce8f29.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/entry/common.c | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index d5eee851071c..08a945d7915e 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -394,8 +394,20 @@ __visible long do_fast_syscall_32(struct pt_regs *regs) * WARNING: We are in CONTEXT_USER and RCU isn't paying attention! */ local_irq_enable(); - if (get_user(*(u32 *)®s->cx, - (u32 __user __force *)(unsigned long)(u32)regs->sp)) { + if ( +#ifdef CONFIG_X86_64 + /* + * Micro-optimization: the pointer we're following is explicitly + * 32 bits, so it can't be out of range. + */ + __get_user(*(u32 *)®s->cx, + (u32 __user __force *)(unsigned long)(u32)regs->sp) +#else + get_user(*(u32 *)®s->cx, + (u32 __user __force *)(unsigned long)(u32)regs->sp) +#endif + ) { + /* User code screwed up. */ local_irq_disable(); regs->ax = -EFAULT; |