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>

diff --git a/Documentation/virtual/kvm/devices/vcpu.txt b/Documentation/virtual/kvm/devices/vcpu.txt
index c04165868faff91dc25f99693bad788afb33f9a3..02f50686c41854f7fc2ce054a368ddaa4f8a9dc5 100644 (file)
--- a/Documentation/virtual/kvm/devices/vcpu.txt
+++ b/Documentation/virtual/kvm/devices/vcpu.txt
@@ -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.

diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index a027569facfae948ef562d11604c162dc0d96c1e..6e9c40eea208a2e2e2f7e36e45dc7fc3329f5169 100644 (file)
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -423,6 +423,14 @@ static int kvm_arm_pmu_v3_init(struct kvm_vcpu *vcpu)
        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;