[PATCH] KVM: arm/arm64: Fix bug when registering redist iodevs

[eric.auger@redhat.com (Auger Eric)]

Hi Christoffer,

On 17/05/2017 15:17, Christoffer Dall wrote:
> If userspace creates the VCPUs after initializing the VGIC, then we end
> up in a situation where we trigger a bug in kvm_vcpu_get_idx(), because
> it is called prior to adding the VCPU into the vcpus array on the VM.
> 
> There is no tight coupling between the VCPU index and the area of the
> redistributor region used for the VCPU, so we can simply ensure that all
> creations of redistributors are serialized per VM, and increment an
> offset when we successfully add a redistributor.
> 
> The vgic_register_redist_iodev() function can be called from two paths:
> vgic_redister_all_redist_iodev() which is called via the kvm_vgic_addr()
> device attribute handler.  This patch already holds the kvm->lock mutex.
> 
> The other path is via kvm_vgic_vcpu_init, which is called through a
> longer chain from kvm_vm_ioctl_create_vcpu(), which releases the
> kvm->lock mutex just before calling kvm_arch_vcpu_create(), so we can
> simply take this mutex again later for our purposes.
> 
> Fixes: ab6f468c10 ("KVM: arm/arm64: Register iodevs when setting redist base and creating VCPUs")
> Signed-off-by: Christoffer Dall <cdall@linaro.org>
> Tested-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Thanks

Eric
> ---
>  include/kvm/arm_vgic.h           | 5 ++++-
>  virt/kvm/arm/vgic/vgic-init.c    | 5 ++++-
>  virt/kvm/arm/vgic/vgic-mmio-v3.c | 9 ++++++---
>  3 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index 97b8d37..ef71858 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -195,7 +195,10 @@ struct vgic_dist {
>  		/* either a GICv2 CPU interface */
>  		gpa_t			vgic_cpu_base;
>  		/* or a number of GICv3 redistributor regions */
> -		gpa_t			vgic_redist_base;
> +		struct {
> +			gpa_t		vgic_redist_base;
> +			gpa_t		vgic_redist_free_offset;
> +		};
>  	};
>  
>  	/* distributor enabled */
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index dc68e2e..3a0b899 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -242,8 +242,11 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
>  	 * If we are creating a VCPU with a GICv3 we must also register the
>  	 * KVM io device for the redistributor that belongs to this VCPU.
>  	 */
> -	if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3)
> +	if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3) {
> +		mutex_lock(&vcpu->kvm->lock);
>  		ret = vgic_register_redist_iodev(vcpu);
> +		mutex_unlock(&vcpu->kvm->lock);
> +	}
>  	return ret;
>  }
>  
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> index 99da1a2..9b0f681 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -586,7 +586,7 @@ int vgic_register_redist_iodev(struct kvm_vcpu *vcpu)
>  	if (!vgic_v3_check_base(kvm))
>  		return -EINVAL;
>  
> -	rd_base = vgic->vgic_redist_base + kvm_vcpu_get_idx(vcpu) * SZ_64K * 2;
> +	rd_base = vgic->vgic_redist_base + vgic->vgic_redist_free_offset;
>  	sgi_base = rd_base + SZ_64K;
>  
>  	kvm_iodevice_init(&rd_dev->dev, &kvm_io_gic_ops);
> @@ -615,11 +615,14 @@ int vgic_register_redist_iodev(struct kvm_vcpu *vcpu)
>  	ret = kvm_io_bus_register_dev(kvm, KVM_MMIO_BUS, sgi_base,
>  				      SZ_64K, &sgi_dev->dev);
>  	mutex_unlock(&kvm->slots_lock);
> -	if (ret)
> +	if (ret) {
>  		kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS,
>  					  &rd_dev->dev);
> +		return ret;
> +	}
>  
> -	return ret;
> +	vgic->vgic_redist_free_offset += 2 * SZ_64K;
> +	return 0;
>  }
>  
>  static void vgic_unregister_redist_iodev(struct kvm_vcpu *vcpu)
>