diff options
| author | Andy Lutomirski <luto@kernel.org> | 2015-10-05 17:48:20 -0700 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-10-09 09:41:12 +0200 |
| commit | c68ca6787bdd6d2df37cf950135aa11e71af358a (patch) | |
| tree | e4c1c92be7f20cd4dc4b74ed605d494bc4154afb /arch/x86/entry/common.c | |
| parent | 33c52129f45e06d9ce23e1a3d50bf9fd6770748b (diff) | |
| download | lwn-c68ca6787bdd6d2df37cf950135aa11e71af358a.tar.gz lwn-c68ca6787bdd6d2df37cf950135aa11e71af358a.zip | |
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 <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.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry/common.c')
| -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; |