Commit c68ca678 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

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: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/bdff034e2f23c5eb974c760cf494cb5bddce8f29.1444091585.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 33c52129
...@@ -394,8 +394,20 @@ __visible long do_fast_syscall_32(struct pt_regs *regs) ...@@ -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! * WARNING: We are in CONTEXT_USER and RCU isn't paying attention!
*/ */
local_irq_enable(); local_irq_enable();
if (get_user(*(u32 *)&regs->cx, if (
(u32 __user __force *)(unsigned long)(u32)regs->sp)) { #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 *)&regs->cx,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#else
get_user(*(u32 *)&regs->cx,
(u32 __user __force *)(unsigned long)(u32)regs->sp)
#endif
) {
/* User code screwed up. */ /* User code screwed up. */
local_irq_disable(); local_irq_disable();
regs->ax = -EFAULT; regs->ax = -EFAULT;
......
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