Re: [PATCH v3 9/9] KVM: arm/arm64: Don't assume initialized vgic when setting PMU IRQ

Marc Zyngier
2017-06-08T14:31:00Z

On Thu, Jun 08 2017 at 3:34:46 pm BST, Christoffer Dall <cdall@linaro.org> wrote:
> The PMU IRQ number is set through the VCPU device's KVM_SET_DEVICE_ATTR
> ioctl handler for the KVM_ARM_VCPU_PMU_V3_IRQ attribute, but there is no
> enforced or stated requirement that this must happen after initializing
> the VGIC. As a result, calling vgic_valid_spi() which relies on the
> nr_spis being set during the VGIC init can incorrectly fail.
>
> Introduce irq_is_spi, which determines if an IRQ number is within the
> SPI range without verifying it against the actual VGIC properties.
>
> Signed-off-by: Christoffer Dall <cdall@linaro.org>
> ---
> include/kvm/arm_vgic.h | 2 ++
> virt/kvm/arm/pmu.c | 2 +-
> 2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 131668f..a2ae9d2 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -39,6 +39,8 @@
> #define KVM_IRQCHIP_NUM_PINS (1020 - 32)
>
> #define irq_is_ppi(irq) ((irq) >= VGIC_NR_SGIS && (irq) < VGIC_NR_PRIVATE_IRQS)
> +#define irq_is_spi(irq) ((irq) >= VGIC_NR_PRIVATE_IRQS && \
> + (irq) <= VGIC_MAX_SPI)
>
> enum vgic_type {
> VGIC_V2, /* Good ol' GICv2 */
> diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
> index 26a42a9..87cb325 100644
> --- a/virt/kvm/arm/pmu.c
> +++ b/virt/kvm/arm/pmu.c
> @@ -547,7 +547,7 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> return -EFAULT;
>
> /* The PMU overflow interrupt can be a PPI or a valid SPI. */
> - if (!(irq_is_ppi(irq) || vgic_valid_spi(vcpu->kvm, irq)))
> + if (!(irq_is_ppi(irq) || irq_is_spi(irq)))
> return -EINVAL;
>
> if (!pmu_irq_is_valid(vcpu->kvm, irq))

Does it mean that we can now fail an injection if the SPI is out of the
range of configured SPIs?

If that's the case, the WARN_ON() in kvm_pmu_update_state() is going to
fire badly, and that's going to be ugly. Should we add a check for this
case in kvm_arm_pmu_v3_init()?

Thanks,

M.
--
Jazz is not dead, it just smell funny.