arm64: kernel: Init MDCR_EL2 even in the absence of a PMU

Commit f436b2ac90a0 ("arm64: kernel: fix architected PMU registers
unconditional access") made sure we wouldn't access unimplemented
PMU registers, but also left MDCR_EL2 uninitialized in that case,
leading to trap bits being potentially left set.

Make sure we always write something in that register.

Fixes: f436b2ac90a0 ("arm64: kernel: fix architected PMU registers unconditional access")
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 427f6d3..332e331 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -586,8 +586,9 @@ CPU_LE(     movk    x0, #0x30d0, lsl #16    )       // Clear EE and E0E on LE systems
        b.lt    4f                              // Skip if no PMU present
        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
 4:
+       csel    x0, xzr, x0, lt                 // all PMU counters from EL1
+       msr     mdcr_el2, x0                    // (if they exist)
 
        /* Stage-2 translation */
        msr     vttbr_el2, xzr