[PATCH 3.16.y-ckt 051/118] x86/nmi/64: Remove asm code that saves CR2

[Luis Henriques]

3.16.7-ckt16 -stable review patch.  If anyone has any objections, please let me know.

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

From: Andy Lutomirski <luto at kernel.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 at kernel.org>
Reviewed-by: Steven Rostedt <rostedt at goodmis.org>
Acked-by: Borislav Petkov <bp at suse.de>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Ingo Molnar <mingo at kernel.org>
[bwh: Backported to 4.0: adjust filename, context]
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
[ luis: backported to 3.16: used Ben's backport to 4.0 ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/x86/kernel/entry_64.S | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index c0ec84a1890e..5ee10d35d79f 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1636,29 +1636,11 @@ 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
 nmi_swapgs: