[added to the 4.1 stable tree] arm64: mdscr_el1: avoid exposing DCC to userspace

From: Will Deacon <redacted>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit d8d23fa0f27f3b2942a7bbc7378c7735324ed519 ]

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 <redacted>
Signed-off-by: Sasha Levin <redacted>
---
 arch/arm64/mm/proc.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index cdd754e..d2c2e3b 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S

@@ -202,7 +202,8 @@ 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:
 	 *

-- 
2.5.0