linux-kernel - [tip:x86/asm] x86/syscalls: Don't pointlessly reload the system call number

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Date:   Fri, 6 Apr 2018 10:09:56 -0700
From:   tip-bot for Linus Torvalds <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org, jpoimboe@...hat.com,
        brgerst@...il.com, luto@...nel.org, hpa@...or.com, bp@...en8.de,
        mingo@...nel.org, dvlasenk@...hat.com, linux@...inikbrodowski.net,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [tip:x86/asm] x86/syscalls: Don't pointlessly reload the system
 call number

Commit-ID:  dfe64506c01e57159a4c550fe537c13a317ff01b
Gitweb:     https://git.kernel.org/tip/dfe64506c01e57159a4c550fe537c13a317ff01b
Author:     Linus Torvalds <torvalds@...ux-foundation.org>
AuthorDate: Thu, 5 Apr 2018 11:53:00 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 5 Apr 2018 16:59:24 +0200

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@...ux-foundation.org>
Signed-off-by: Dominik Brodowski <linux@...inikbrodowski.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20180405095307.3730-2-linux@dominikbrodowski.net
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/entry/common.c   | 12 ++++++------
 arch/x86/entry/entry_64.S |  3 ++-
 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 */