Re: [PATCH v3 41/59] KVM: arm/arm64: GICv4: Wire mapping/unmapping of VLPIs in VFIO irq bypass

Auger Eric
2017-08-30T10:18:48Z

Hi Marc,

On 30/08/2017 11:42, Marc Zyngier wrote:
> On 26/08/17 20:48, Christoffer Dall wrote:
>> On Mon, Jul 31, 2017 at 06:26:19PM +0100, Marc Zyngier wrote:
>>> Let's use the irq bypass mechanism introduced for platform device
>>> interrupts to intercept the virtual PCIe endpoint configuration
>>> and establish our LPI->VLPI mapping.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>> ---
>>> include/kvm/arm_vgic.h | 8 ++++
>>> virt/kvm/arm/arm.c | 27 ++++++++----
>>> virt/kvm/arm/vgic/vgic-v4.c | 103 ++++++++++++++++++++++++++++++++++++++++++++
>>> 3 files changed, 130 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>>> index 359eeffe9857..050f78d4fb42 100644
>>> --- a/include/kvm/arm_vgic.h
>>> +++ b/include/kvm/arm_vgic.h
>>> @@ -367,4 +367,12 @@ int kvm_vgic_set_forwarding(struct kvm *kvm, unsigned int host_irq,
>>> void kvm_vgic_unset_forwarding(struct kvm *kvm, unsigned int host_irq,
>>> unsigned int vintid);
>>>
>>> +struct kvm_kernel_irq_routing_entry;
>>> +
>>> +int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int irq,
>>> + struct kvm_kernel_irq_routing_entry *irq_entry);
>>> +
>>> +int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
>>> + struct kvm_kernel_irq_routing_entry *irq_entry);
>>> +
>>> #endif /* __KVM_ARM_VGIC_H */
>>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>>> index ebab6c29e3be..6803ea27c47d 100644
>>> --- a/virt/kvm/arm/arm.c
>>> +++ b/virt/kvm/arm/arm.c
>>> @@ -1457,11 +1457,16 @@ int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
>>> struct kvm_kernel_irqfd *irqfd =
>>> container_of(cons, struct kvm_kernel_irqfd, consumer);
>>>
>>> - if (prod->type != IRQ_BYPASS_VFIO_PLATFORM)
>>> + switch (prod->type) {
>>> + case IRQ_BYPASS_VFIO_PLATFORM:
>>> + return kvm_vgic_set_forwarding(irqfd->kvm, prod->irq,
>>> + irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>> + case IRQ_BYPASS_VFIO_PCI_MSI:
>>> + return kvm_vgic_v4_set_forwarding(irqfd->kvm, prod->irq,
>>> + &irqfd->irq_entry);
>>> + default:
>>> return 0;
>>> -
>>> - return kvm_vgic_set_forwarding(irqfd->kvm, prod->irq,
>>> - irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>> + }
>>> }
>>> void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
>>> struct irq_bypass_producer *prod)
>>> @@ -1469,11 +1474,17 @@ void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,
>>> struct kvm_kernel_irqfd *irqfd =
>>> container_of(cons, struct kvm_kernel_irqfd, consumer);
>>>
>>> - if (prod->type != IRQ_BYPASS_VFIO_PLATFORM)
>>> - return;
>>> + switch (prod->type) {
>>> + case IRQ_BYPASS_VFIO_PLATFORM:
>>> + kvm_vgic_unset_forwarding(irqfd->kvm, prod->irq,
>>> + irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>> + break;
>>>
>>> - kvm_vgic_unset_forwarding(irqfd->kvm, prod->irq,
>>> - irqfd->gsi + VGIC_NR_PRIVATE_IRQS);
>>> + case IRQ_BYPASS_VFIO_PCI_MSI:
>>> + kvm_vgic_v4_unset_forwarding(irqfd->kvm, prod->irq,
>>> + &irqfd->irq_entry);
>>> + break;
>>> + }
>>> }
>>>
>>> void kvm_arch_irq_bypass_stop(struct irq_bypass_consumer *cons)
>>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
>>> index 207e1fda0dcd..338c86c5159f 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v4.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
>>> @@ -72,3 +72,106 @@ void vgic_v4_teardown(struct kvm *kvm)
>>> its_vm->nr_vpes = 0;
>>> its_vm->vpes = NULL;
>>> }
>>> +
>>> +static struct vgic_its *vgic_get_its(struct kvm *kvm,
>>> + struct kvm_kernel_irq_routing_entry *irq_entry)
>>> +{
>>> + struct kvm_msi msi = (struct kvm_msi) {
>>> + .address_lo = irq_entry->msi.address_lo,
>>> + .address_hi = irq_entry->msi.address_hi,
>>> + .data = irq_entry->msi.data,
>>> + .flags = irq_entry->msi.flags,
>>> + .devid = irq_entry->msi.devid,
>>> + };
>>> +
>>> + /*
>>> + * Get a reference on the LPI. If NULL, this is not a valid
>>> + * translation for any of our vITSs.
>>> + */
>>> + return vgic_msi_to_its(kvm, &msi);
>>> +}
>>> +
>>> +int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
>>> + struct kvm_kernel_irq_routing_entry *irq_entry)
>>> +{
>>> + struct vgic_its *its;
>>> + struct vgic_irq *irq;
>>> + struct its_vlpi_map map;
>>> + int ret;
>>> +
>>> + if (!vgic_is_v4_capable(kvm))
>>> + return 0;
>>> +
>>> + /*
>>> + * Get the ITS, and escape early on error (not a valid
>>> + * doorbell for any of our vITSs).
>>> + */
>>> + its = vgic_get_its(kvm, irq_entry);
>>> + if (IS_ERR(its))
>>> + return 0;
>>> +
>>> + mutex_lock(&its->its_lock);
>>> +
>>> + /* Perform then actual DevID/EventID -> LPI translation. */
>>> + ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
>>> + irq_entry->msi.data, &irq);
>>> + if (ret)
>>> + goto out;
>>> +
>>> + /*
>>> + * Emit the mapping request. If it fails, the ITS probably
>>> + * isn't v4 compatible, so let's silently bail out. Holding
>>> + * the ITS lock should ensure that nothing can modify the
>>> + * target vcpu.
>>> + */
>>> + map = (struct its_vlpi_map) {
>>> + .vm = &kvm->arch.vgic.its_vm,
>>> + .vintid = irq->intid,
>>> + .db_enabled = true,
>>> + .vpe_idx = irq->target_vcpu->vcpu_id,
>>> + };
>>> +
>>> + if (its_map_vlpi(virq, &map))
>>> + goto out;
>>
>> This seems to be able to return things like -ENOMEM, whould we really
>> not report this back to the caller in any way?
>
>
> That's a good question.
>
> If we return -ENOMEM, we'll probably end-up returning an error to
> userspace (as a result of the VFIO ioctl), which will in turn probably
> terminate the guest (I'm guessing, I haven't actually looked at what
> userspace does).
>
> If we don't return the error, then we have a chance to keep the guest
> running by sticking to software injection.
I have not read the whole stuff yet but userspace is not aware of this
negotiation. Everything happens under the hood in kernel, see
virt/lib/irqbypass.c __connect(): if add_producer() fails
prod->del_consumer() is called and we should return to the not optimized
injection.

Thanks

Eric
>
> I'm not sure what is preferable...
>
> Thanks,
>
> M.
>