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

Marc Zyngier
2017-08-30T09:42:58Z

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'm not sure what is preferable...

Thanks,

M.
--
Jazz is not dead. It just smells funny...