From d8d23fa0f27f3b2942a7bbc7378c7735324ed519 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Thu, 20 Aug 2015 11:47:13 +0100
Subject: arm64: mdscr_el1: avoid exposing DCC to userspace

We don't want to expose the DCC to userspace, particularly as there is
a kernel console driver for it.

This patch resets mdscr_el1 to disable userspace access to the DCC
registers on the cold boot path.

Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 6e8765a..e4ee7bd 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -151,7 +151,8 @@ ENTRY(__cpu_setup)
 
 	mov	x0, #3 << 20
 	msr	cpacr_el1, x0			// Enable FP/ASIMD
-	msr	mdscr_el1, xzr			// Reset mdscr_el1
+	mov	x0, #1 << 12			// Reset mdscr_el1 and disable
+	msr	mdscr_el1, x0			// access to the DCC from EL0
 	/*
 	 * Memory region attributes for LPAE:
 	 *
-- 
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