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Commit 6fe407f2 authored Sep 26, 2016 by Christoffer Dall

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



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.

Cc: stable@vger.kernel.org
Cc: Shannon Zhao <shannon.zhao@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

parent 3d9cd95f

Documentation/virtual/kvm/devices/vcpu.txt

+3 −1

Original line number	Original line	Diff line number	Diff line
	@@ -30,4 +30,6 @@ Returns: -ENODEV: PMUv3 not supported
	attribute		attribute
	-EBUSY: PMUv3 already initialized		-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.

virt/kvm/arm/pmu.c

+8 −0

Original line number	Original line	Diff line number	Diff line
	@@ -423,6 +423,14 @@ static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu)
	if (!kvm_arm_support_pmu_v3())		if (!kvm_arm_support_pmu_v3())
	return -ENODEV;		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) \|\|		if (!test_bit(KVM_ARM_VCPU_PMU_V3, vcpu->arch.features) \|\|
	!kvm_arm_pmu_irq_initialized(vcpu))		!kvm_arm_pmu_irq_initialized(vcpu))
	return -ENXIO;		return -ENXIO;