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Subject[PATCH][GIT PULL][v3.3] x86: Specify a size for the cmp in the NMI handler
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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@redhat.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@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.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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