x86/entry/64: Migrate the 64-bit syscall slow path to C
This is more complicated than the 32-bit and compat cases
because it preserves an asm fast path for the case where the
callee-saved regs aren't needed in pt_regs and no entry or exit
work needs to be done.
This appears to slow down fastpath syscalls by no more than one
cycle on my Skylake laptop.
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: Frederic Weisbecker <fweisbec@gmail.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>
Link: http://lkml.kernel.org/r/ce2335a4d42dc164b24132ee5e8c7716061f947b.1454022279.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 0366374..75175f9 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -344,6 +344,32 @@
prepare_exit_to_usermode(regs);
}
+#ifdef CONFIG_X86_64
+__visible void do_syscall_64(struct pt_regs *regs)
+{
+ struct thread_info *ti = pt_regs_to_thread_info(regs);
+ unsigned long nr = regs->orig_ax;
+
+ local_irq_enable();
+
+ if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
+ nr = syscall_trace_enter(regs);
+
+ /*
+ * NB: Native and x32 syscalls are dispatched from the same
+ * table. The only functional difference is the x32 bit in
+ * regs->orig_ax, which changes the behavior of some syscalls.
+ */
+ if (likely((nr & __SYSCALL_MASK) < NR_syscalls)) {
+ regs->ax = sys_call_table[nr & __SYSCALL_MASK](
+ regs->di, regs->si, regs->dx,
+ regs->r10, regs->r8, regs->r9);
+ }
+
+ syscall_return_slowpath(regs);
+}
+#endif
+
#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
/*
* Does a 32-bit syscall. Called with IRQs on and does all entry and