linux-kernel - [PATCH 4/6 v2] x86: entry_64.S: fold test_in

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Message-Id: <1424782358-23816-1-git-send-email-dvlasenk@redhat.com>
Date:	Tue, 24 Feb 2015 13:52:38 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/6 v2] x86: entry_64.S: fold test_in_nmi macro into its only user

No code changes.

Changes since v1: added comments as requested by Steven Rostedt

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Borislav Petkov <bp@...en8.de>
CC: "H. Peter Anvin" <hpa@...or.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Frederic Weisbecker <fweisbec@...il.com>
CC: X86 ML <x86@...nel.org>
CC: Alexei Starovoitov <ast@...mgrid.com>
CC: Will Drewry <wad@...omium.org>
CC: Kees Cook <keescook@...omium.org>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/entry_64.S | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 03498d0..0ec7928 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1378,19 +1378,7 @@ 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
@@ -1426,7 +1414,7 @@ ENTRY(nmi)
 	 * NMI.
 	 */
 
-	/* Use %rdx as out temp variable throughout */
+	/* Use %rdx as our temp variable throughout */
 	pushq_cfi %rdx
 	CFI_REL_OFFSET rdx, 0
 
@@ -1451,8 +1439,18 @@ 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:
-- 
1.8.1.4

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