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

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Date:   Tue,  3 Jan 2017 18:10:21 +0000
From:   Will Deacon <will.deacon@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     marc.zyngier@....com, mark.rutland@....com, kim.phillips@....com,
        alex.bennee@...aro.org, christoffer.dall@...aro.org,
        tglx@...utronix.de, peterz@...radead.org,
        alexander.shishkin@...ux.intel.com, robh@...nel.org,
        suzuki.poulose@....com, pawel.moll@....com,
        mathieu.poirier@...aro.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, Will Deacon <will.deacon@....com>
Subject: [RFC PATCH 04/10] arm64: head.S: Enable EL1 (host) access to SPE when entered at EL2

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