linux-kernel - [PATCH 3.14 78/84] x86/nmi/64: Remove asm code that saves CR2

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Message-Id: <20150929145334.439390942@linuxfoundation.org>
Date:	Tue, 29 Sep 2015 17:19:10 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 3.14 78/84] x86/nmi/64: Remove asm code that saves CR2

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andy Lutomirski <luto@...nel.org>

commit 0e181bb58143cb4a2e8f01c281b0816cd0e4798e upstream.

Now that do_nmi saves CR2, we don't need to save it in asm.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
Reviewed-by: Steven Rostedt <rostedt@...dmis.org>
Acked-by: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>


---
 arch/x86/kernel/entry_64.S |   18 ------------------
 1 file changed, 18 deletions(-)

--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1885,28 +1885,10 @@ end_repeat_nmi:
 	call save_paranoid
 	DEFAULT_FRAME 0
 
-	/*
-	 * Save off the CR2 register. If we take a page fault in the NMI then
-	 * it could corrupt the CR2 value. If the NMI preempts a page fault
-	 * handler before it was able to read the CR2 register, and then the
-	 * NMI itself takes a page fault, the page fault that was preempted
-	 * will read the information from the NMI page fault and not the
-	 * origin fault. Save it off and restore it if it changes.
-	 * Use the r12 callee-saved register.
-	 */
-	movq %cr2, %r12
-
 	/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
 	movq %rsp,%rdi
 	movq $-1,%rsi
 	call do_nmi
-
-	/* Did the NMI take a page fault? Restore cr2 if it did */
-	movq %cr2, %rcx
-	cmpq %rcx, %r12
-	je 1f
-	movq %r12, %cr2
-1:
 	
 	testl %ebx,%ebx				/* swapgs needed? */
 	jnz nmi_restore


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