[tip:x86/cpu] x86/entry/64: Don't compile ignore_sysret if 32-bit emulation is enabled

[tip-bot for Andy Lutomirski]

Commit-ID:  dffb3f9db6b593f3ed6ab4c8d8f10e0aa6aa7a88
Gitweb:     https://git.kernel.org/tip/dffb3f9db6b593f3ed6ab4c8d8f10e0aa6aa7a88
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Mon, 1 Jul 2019 20:43:20 -0700
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 2 Jul 2019 08:45:20 +0200

x86/entry/64: Don't compile ignore_sysret if 32-bit emulation is enabled

It's only used if !CONFIG_IA32_EMULATION, so disable it in normal
configs.  This will save a few bytes of text and reduce confusion.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc:  "BaeChang Seok" <chang.seok.bae@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: "Bae, Chang Seok" <chang.seok.bae@xxxxxxxxx>
Link: https://lkml.kernel.org/r/0f7dafa72fe7194689de5ee8cfe5d83509fabcf5.1562035429.git.luto@xxxxxxxxxx

---
 arch/x86/entry/entry_64.S | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 7f9f5119d6b1..54b1b0468b2b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1743,11 +1743,17 @@ nmi_restore:
 	iretq
 END(nmi)
 
+#ifndef CONFIG_IA32_EMULATION
+/*
+ * This handles SYSCALL from 32-bit code.  There is no way to program
+ * MSRs to fully disable 32-bit SYSCALL.
+ */
 ENTRY(ignore_sysret)
 	UNWIND_HINT_EMPTY
 	mov	$-ENOSYS, %eax
 	sysret
 END(ignore_sysret)
+#endif
 
 ENTRY(rewind_stack_do_exit)
 	UNWIND_HINT_FUNC