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>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 286efa342091..10868aa734dc 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: