[3.16.y-ckt stable] Patch "x86/asm/entry/64: Fold the 'test_in_nmi' macro into its only user" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    x86/asm/entry/64: Fold the 'test_in_nmi' macro into its only user

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 93148640a2cd59960d0b0bca6d02d39e67a9ca6f Mon Sep 17 00:00:00 2001
From: Denys Vlasenko <dvlasenk at redhat.com>
Date: Wed, 1 Apr 2015 16:50:57 +0200
Subject: x86/asm/entry/64: Fold the 'test_in_nmi' macro into its only user

commit 0784b36448a2a85b95b6eb21a69b9045c896c065 upstream.

No code changes.

Signed-off-by: Denys Vlasenko <dvlasenk at redhat.com>
Acked-by: Borislav Petkov <bp at suse.de>
Cc: Alexei Starovoitov <ast at plumgrid.com>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Kees Cook <keescook at chromium.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Oleg Nesterov <oleg at redhat.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Will Drewry <wad at chromium.org>
Link: http://lkml.kernel.org/r/1427899858-7165-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/entry_64.S | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 94aa18a9cc11..c13aaaac878b 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1423,19 +1423,7 @@ ENTRY(error_exit)
 	CFI_ENDPROC
 END(error_exit)

-/*
- * Test if a given stack is an NMI stack or not.
- */
-	.macro test_in_nmi reg stack nmi_ret normal_ret
-	cmpq %\reg, \stack
-	ja \normal_ret
-	subq $EXCEPTION_STKSZ, %\reg
-	cmpq %\reg, \stack
-	jb \normal_ret
-	jmp \nmi_ret
-	.endm
-
-	/* runs on exception stack */
+/* Runs on exception stack */
 ENTRY(nmi)
 	INTR_FRAME
 	PARAVIRT_ADJUST_EXCEPTION_FRAME
@@ -1496,8 +1484,18 @@ ENTRY(nmi)
 	 * We check the variable because the first NMI could be in a
 	 * breakpoint routine using a breakpoint stack.
 	 */
-	lea 6*8(%rsp), %rdx
-	test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
+	lea	6*8(%rsp), %rdx
+	/* Compare the NMI stack (rdx) with the stack we came from (4*8(%rsp)) */
+	cmpq	%rdx, 4*8(%rsp)
+	/* If the stack pointer is above the NMI stack, this is a normal NMI */
+	ja	first_nmi
+	subq	$EXCEPTION_STKSZ, %rdx
+	cmpq	%rdx, 4*8(%rsp)
+	/* If it is below the NMI stack, it is a normal NMI */
+	jb	first_nmi
+	/* Ah, it is within the NMI stack, treat it as nested */
+	jmp	nested_nmi
+
 	CFI_REMEMBER_STATE

 nested_nmi: