linux-kernel - [RFC 27/30] x86/entry: Remove unnecessary IRQ twiddling in fast 32-bit syscalls

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Message-Id: <2d007cfb72f1d8424b34cbd514f47c4fd8eafb22.1441146105.git.luto@kernel.org>
Date:	Tue,  1 Sep 2015 15:41:27 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...nel.org>
Subject: [RFC 27/30] x86/entry: Remove unnecessary IRQ twiddling in fast 32-bit syscalls

This is slightly messy, but it eliminates an unnecessary cli;sti pair.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/common.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 96bf0e79159e..a050c4c735c3 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -323,10 +323,10 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)
 
 #if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
 /*
- * Does a 32-bit syscall.  Called with IRQs off and does all entry and
- * exit work.
+ * Does a 32-bit syscall.  Called with IRQs on and does all entry and
+ * exit work and returns with IRQs off.
  */
-__visible void do_int80_syscall_32(struct pt_regs *regs)
+static void do_syscall_32_irqs_on(struct pt_regs *regs)
 {
 	struct thread_info *ti = pt_regs_to_thread_info(regs);
 	unsigned int nr = (unsigned int)regs->orig_ax;
@@ -335,8 +335,6 @@ __visible void do_int80_syscall_32(struct pt_regs *regs)
 	ti->status |= TS_COMPAT;
 #endif
 
-	local_irq_enable();
-
 	if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
 		/*
 		 * Subtlety here: if ptrace pokes something larger than
@@ -363,6 +361,13 @@ __visible void do_int80_syscall_32(struct pt_regs *regs)
 	syscall_return_slowpath(regs);
 }
 
+/* Handles int $0x80 */
+__visible void do_int80_syscall_32(struct pt_regs *regs)
+{
+	local_irq_enable();
+	do_syscall_32_irqs_on(regs);
+}
+
 /* Returns 0 to return using IRET or 1 to return using SYSRETL. */
 __visible long do_fast_syscall_32(struct pt_regs *regs)
 {
@@ -394,10 +399,9 @@ __visible long do_fast_syscall_32(struct pt_regs *regs)
 		prepare_exit_to_usermode(regs);
 		return 0;	/* Keep it simple: use IRET. */
 	}
-	local_irq_disable();
 
 	/* Now this is just like a normal syscall. */
-	do_int80_syscall_32(regs);
+	do_syscall_32_irqs_on(regs);
 
 #ifdef CONFIG_X86_64
 	/*
-- 
2.4.3

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