[PATCH 3.16.y-ckt 005/104] arm64: head.S: initialise mdcr_el2 in el2_setup

[Luis Henriques]

3.16.7-ckt19 -stable review patch.  If anyone has any objections, please let me know.

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

From: Will Deacon <will.deacon at arm.com>

commit d10bcd473301888f957ec4b6b12aa3621be78d59 upstream.

When entering the kernel at EL2, we fail to initialise the MDCR_EL2
register which controls debug access and PMU capabilities at EL1.

This patch ensures that the register is initialised so that all traps
are disabled and all the PMU counters are available to the host. When a
guest is scheduled, KVM takes care to configure trapping appropriately.

Acked-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm64/kernel/head.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 1cd11e73058f..a089ce8d52b3 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -315,6 +315,11 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
 	msr	hstr_el2, xzr			// Disable CP15 traps to EL2
 #endif
 
+	/* EL2 debug */
+	mrs	x0, pmcr_el0			// Disable debug access traps
+	ubfx	x0, x0, #11, #5			// to EL2 and allow access to
+	msr	mdcr_el2, x0			// all PMU counters from EL1
+
 	/* Stage-2 translation */
 	msr	vttbr_el2, xzr