[tip:x86/asm] x86/entry/32: Change INT80 to be an interrupt gate

[tip-bot for Andy Lutomirski <tipbot@zytor.com>]

Commit-ID:  a798f091113ef4999277dbe0483d37d04fa35b2e
Gitweb:     http://git.kernel.org/tip/a798f091113ef4999277dbe0483d37d04fa35b2e
Author:     Andy Lutomirski <luto@kernel.org>
AuthorDate: Wed, 9 Mar 2016 13:24:32 -0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 10 Mar 2016 10:53:26 +0100

x86/entry/32: Change INT80 to be an interrupt gate

We want all of the syscall entries to run with interrupts off so that
we can efficiently run context tracking before enabling interrupts.

This will regress int $0x80 performance on 32-bit kernels by a
couple of cycles.  This shouldn't matter much -- int $0x80 is not a
fast path.

This effectively reverts:

  657c1eea0019 ("x86/entry/32: Fix entry_INT80_32() to expect interrupts to be on")

... and fixes the same issue differently.

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: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/59b4f90c9ebfccd8c937305dbbbca680bc74b905.1457558566.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/entry/common.c          | 15 +++------------
 arch/x86/entry/entry_32.S        |  8 ++++----
 arch/x86/entry/entry_64_compat.S |  2 +-
 arch/x86/kernel/traps.c          |  2 +-
 4 files changed, 9 insertions(+), 18 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 209ba33..d69d1b6 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -371,14 +371,7 @@ __visible void do_syscall_64(struct pt_regs *regs)
  * in workloads that use it, and it's usually called from
  * do_fast_syscall_32, so forcibly inline it to improve performance.
  */
-#ifdef CONFIG_X86_32
-/* 32-bit kernels use a trap gate for INT80, and the asm code calls here. */
-__visible
-#else
-/* 64-bit kernels use do_syscall_32_irqs_off() instead. */
-static
-#endif
-__always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
+static __always_inline 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;
@@ -413,14 +406,12 @@ __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
 	syscall_return_slowpath(regs);
 }
 
-#ifdef CONFIG_X86_64
-/* Handles INT80 on 64-bit kernels */
-__visible void do_syscall_32_irqs_off(struct pt_regs *regs)
+/* Handles int $0x80 */
+__visible void do_int80_syscall_32(struct pt_regs *regs)
 {
 	local_irq_enable();
 	do_syscall_32_irqs_on(regs);
 }
-#endif
 
 /* Returns 0 to return using IRET or 1 to return using SYSEXIT/SYSRETL. */
 __visible long do_fast_syscall_32(struct pt_regs *regs)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 286efa3..10868aa 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -463,13 +463,13 @@ ENTRY(entry_INT80_32)
 	SAVE_ALL pt_regs_ax=$-ENOSYS	/* save rest */
 
 	/*
-	 * User mode is traced as though IRQs are on.  Unlike the 64-bit
-	 * case, INT80 is a trap gate on 32-bit kernels, so interrupts
-	 * are already on (unless user code is messing around with iopl).
+	 * User mode is traced as though IRQs are on, and the interrupt gate
+	 * turned them off.
 	 */
+	TRACE_IRQS_OFF
 
 	movl	%esp, %eax
-	call	do_syscall_32_irqs_on
+	call	do_int80_syscall_32
 .Lsyscall_32_done:
 
 restore_all:
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index efe0fe3..847f2f0 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -336,7 +336,7 @@ ENTRY(entry_INT80_compat)
 	TRACE_IRQS_OFF
 
 	movq	%rsp, %rdi
-	call	do_syscall_32_irqs_off
+	call	do_int80_syscall_32
 .Lsyscall_32_done:
 
 	/* Go back to user mode. */
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 49e2e77..5fae2d8 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -912,7 +912,7 @@ void __init trap_init(void)
 #endif
 
 #ifdef CONFIG_X86_32
-	set_system_trap_gate(IA32_SYSCALL_VECTOR, entry_INT80_32);
+	set_system_intr_gate(IA32_SYSCALL_VECTOR, entry_INT80_32);
 	set_bit(IA32_SYSCALL_VECTOR, used_vectors);
 #endif