Re: [PATCH v5 24/26] KVM: arm/arm64: GICv4: Prevent userspace from changing doorbell affinity

Auger Eric
2017-11-07T22:17:51Z

Hi,

On 27/10/2017 16:28, Marc Zyngier wrote:
> We so far allocate the doorbell interrupts without taking any
> special measure regarding the affinity of these interrupts. We
> simply move them around as required when the vcpu gets scheduled
> on a different CPU.
>
> But that's counting without userspace (and the evil irqbalance) that
> can try and move the VPE interrupt around, causing the ITS code
> to emit VMOVP commands and remap the doorbell to another redistributor.
> Worse, this can happen while the vcpu is running, causing all kind
> of trouble if the VPE is already resident, and we end-up in UNPRED
> territory.
>
> So let's take a definitive action and prevent userspace from messing
> with us. This is just a matter of adding IRQ_NO_BALANCING to the
> set of flags we already have, letting the kernel in sole control
> of the affinity.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric
> ---
> virt/kvm/arm/vgic/vgic-v4.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> index d7fe610bb1f5..d10e18eabd3b 100644
> --- a/virt/kvm/arm/vgic/vgic-v4.c
> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> @@ -23,6 +23,8 @@
>
> #include "vgic.h"
>
> +#define DB_IRQ_FLAGS (IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY | IRQ_NO_BALANCING)
> +
> static irqreturn_t vgic_v4_doorbell_handler(int irq, void *info)
> {
> struct kvm_vcpu *vcpu = info;
> @@ -83,7 +85,7 @@ int vgic_v4_init(struct kvm *kvm)
> * doorbell could kick us out of the guest too
> * early...
> */
> - irq_set_status_flags(irq, IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY);
> + irq_set_status_flags(irq, DB_IRQ_FLAGS);
> ret = request_irq(irq, vgic_v4_doorbell_handler,
> 0, "vcpu", vcpu);
> if (ret) {
> @@ -121,7 +123,7 @@ void vgic_v4_teardown(struct kvm *kvm)
> struct kvm_vcpu *vcpu = kvm_get_vcpu(kvm, i);
> int irq = its_vm->vpes[i]->irq;
>
> - irq_clear_status_flags(irq, IRQ_NOAUTOEN | IRQ_DISABLE_UNLAZY);
> + irq_clear_status_flags(irq, DB_IRQ_FLAGS);
> free_irq(irq, vcpu);
> }
>
>