[RFC PATCH 04/10] arm64: head.S: Enable EL1 (host) access to SPE when entered at EL2

[Will Deacon]

The SPE architecture requires each exception level to enable access
to the SPE controls for the exception level below it, since additional
context-switch logic may be required to handle the buffer safely.

This patch allows EL1 (host) access to the SPE controls when entered at
EL2.

Cc: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
 arch/arm64/kernel/head.S | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 4b1abac3485a..6a97831dcf3b 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -592,8 +592,8 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
 #endif
 
 	/* EL2 debug */
-	mrs	x0, id_aa64dfr0_el1		// Check ID_AA64DFR0_EL1 PMUVer
-	sbfx	x0, x0, #8, #4
+	mrs	x1, id_aa64dfr0_el1		// Check ID_AA64DFR0_EL1 PMUVer
+	sbfx	x0, x1, #8, #4
 	cmp	x0, #1
 	b.lt	4f				// Skip if no PMU present
 	mrs	x0, pmcr_el0			// Disable debug access traps
@@ -601,6 +601,16 @@ CPU_LE(	movk	x0, #0x30d0, lsl #16	)	// Clear EE and E0E on LE systems
 4:
 	csel	x0, xzr, x0, lt			// all PMU counters from EL1
 	msr	mdcr_el2, x0			// (if they exist)
+	/* Statistical profiling */
+	ubfx	x0, x1, #32, #4			// Check ID_AA64DFR0_EL1 PMSVer
+	cbz	x0, 5f				// Skip if SPE not present
+	mrs	x0, mdcr_el2			// Preserve HPMN field
+	cmp	x2, xzr				// If VHE is not enabled,
+	mov	x1, #3				// use EL1&0 translations,
+	cinc	x1, x1, ne			// otherwise use EL2 and
+	bfi	x0, x1, #12, #3			// enable/disable access
+	msr	mdcr_el2, x0			// traps accordingly.
+5:
 
 	/* Stage-2 translation */
 	msr	vttbr_el2, xzr
-- 
2.1.4