linux-kernel - [PATCH][GIT PULL][v3.3] x86: Specify a size for the cmp in the NMI handler

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Message-ID: <1329781367.25686.45.camel@gandalf.stny.rr.com>
Date:	Mon, 20 Feb 2012 18:42:47 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH][GIT PULL][v3.3] x86: Specify a size for the cmp in the NMI
 handler


Ingo,

Please pull the latest tip/x86/urgent tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/x86/urgent

Head SHA1: 869d49dc575a9cf7041e535ea4911a511bbee764


Steven Rostedt (1):
      x86: Specify a size for the cmp in the NMI handler

----
 arch/x86/kernel/entry_64.S |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---------------------------
commit 869d49dc575a9cf7041e535ea4911a511bbee764
Author: Steven Rostedt <srostedt@...hat.com>
Date:   Mon Feb 20 15:29:34 2012 -0500

    x86: Specify a size for the cmp in the NMI handler
    
    Linus noticed that the cmp used to check if the code segment is
    __KERNEL_CS or not did not specify a size. Perhaps it does not matter
    as H. Peter Anvin noted that user space can not set the bottom two
    bits of the %cs register. But it's best not to let the assembly choose
    and change things between different versions of gas, but instead just
    pick the size.
    
    The full 8 bytes is used to compare the saved code segment against
    __KERNEL_CS. Perhaps this might mess up Xen, but we can fix that when
    the time comes.
    
    Also I noticed that there was another non-specified cmp that checks
    the special stack variable if it is 1 or 0. This too probably doesn't
    matter what cmp is used, but this patch uses cmpl just to make it non
    ambiguous.
    
    Link: http://lkml.kernel.org/r/CA+55aFxfAn9MWRgS3O5k2tqN5ys1XrhSFVO5_9ZAoZKDVgNfGA@mail.gmail.com
    
    Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
    Cc: H. Peter Anvin <hpa@...or.com>
    Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index debd851..666f2cb 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1535,14 +1535,14 @@ ENTRY(nmi)
 	 * If %cs was not the kernel segment, then the NMI triggered in user
 	 * space, which means it is definitely not nested.
 	 */
-	cmp $__KERNEL_CS, 16(%rsp)
+	cmpq $__KERNEL_CS, 16(%rsp)
 	jne first_nmi
 
 	/*
 	 * Check the special variable on the stack to see if NMIs are
 	 * executing.
 	 */
-	cmp $1, -8(%rsp)
+	cmpl $1, -8(%rsp)
 	je nested_nmi
 
 	/*


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