x86/syscalls: Don't pointlessly reload the system call number

We have it in a register in the low-level asm, just pass it in as an
argument rather than have do_syscall_64() load it back in from the
ptregs pointer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Andy Lutomirski <luto@kernel.org>
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: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180405095307.3730-2-linux@dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 8 insertions, 7 deletions

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 74f6eee15179..a8b066dbbf48 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -266,14 +266,13 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 }
 
 #ifdef CONFIG_X86_64
-__visible void do_syscall_64(struct pt_regs *regs)
+__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
 {
-        struct thread_info *ti = current_thread_info();
-        unsigned long nr = regs->orig_ax;
+        struct thread_info *ti;
 
         enter_from_user_mode();
         local_irq_enable();
-
+        ti = current_thread_info();
         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
                 nr = syscall_trace_enter(regs);
 
@@ -282,8 +281,9 @@ __visible void do_syscall_64(struct pt_regs *regs)
          * 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)) {
-                nr = array_index_nospec(nr & __SYSCALL_MASK, NR_syscalls);
+        nr &= __SYSCALL_MASK;
+        if (likely(nr < NR_syscalls)) {
+                nr = array_index_nospec(nr, NR_syscalls);
                 regs->ax = sys_call_table[nr](
                         regs->di, regs->si, regs->dx,
                         regs->r10, regs->r8, regs->r9);
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 936e19642eab..6cfe38665f3c 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -233,7 +233,8 @@ GLOBAL(entry_SYSCALL_64_after_hwframe)
         TRACE_IRQS_OFF
 
         /* IRQs are off. */
-        movq    %rsp, %rdi
+        movq    %rax, %rdi
+        movq    %rsp, %rsi
         call    do_syscall_64           /* returns with IRQs disabled */
 
         TRACE_IRQS_IRETQ                /* we're about to change IF */