Patch "KVM: arm64: Require in-kernel irqchip for PMU support" has been added to the 4.8-stable tree

This is a note to let you know that I've just added the patch titled

KVM: arm64: Require in-kernel irqchip for PMU support

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-arm64-require-in-kernel-irqchip-for-pmu-support.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Christoffer Dall <[email protected]>
Date: Mon, 26 Sep 2016 18:51:47 -0700
Subject: KVM: arm64: Require in-kernel irqchip for PMU support

From: Christoffer Dall <[email protected]>

commit 6fe407f2d18a4f94216263f91cb7d1f08fa5887c upstream.

If userspace creates a PMU for the VCPU, but doesn't create an in-kernel irqchip, then we end up in a nasty path where we try to take an uninitialized spinlock, which can lead to all sorts of breakages.

Luckily, QEMU always creates the VGIC before the PMU, so we can establish this as ABI and check for the VGIC in the PMU init stage. This can be relaxed at a later time if we want to support PMU with a userspace irqchip.

---
 Documentation/virtual/kvm/devices/vcpu.txt |    4 +++-
 virt/kvm/arm/pmu.c                         |    8 ++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

@@ -30,4 +30,6 @@ Returns: -ENODEV: PMUv3 not supported
                  attribute
          -EBUSY: PMUv3 already initialized
 
-Request the initialization of the PMUv3.
+Request the initialization of the PMUv3.  This must be done after creating the
+in-kernel irqchip.  Creating a PMU with a userspace irqchip is currently not
+supported.

@@ -423,6 +423,14 @@ static int kvm_arm_pmu_v3_init(struct kv
 	if (!kvm_arm_support_pmu_v3())
 		return -ENODEV;
 
+	/*
+	 * We currently require an in-kernel VGIC to use the PMU emulation,
+	 * because we do not support forwarding PMU overflow interrupts to
+	 * userspace yet.
+	 */
+	if (!irqchip_in_kernel(vcpu->kvm) || !vgic_initialized(vcpu->kvm))
+		return -ENODEV;
+
 	if (!test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features) ||
 	    !kvm_arm_pmu_irq_initialized(vcpu))
 		return -ENXIO;

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/kvm-arm64-require-in-kernel-irqchip-for-pmu-support.patch queue-4.8/kvm-arm-arm64-vgic-don-t-flush-sync-without-a-working-vgic.patch