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

Marc Zyngier
2017-08-30T10:40:40Z

Hi Eric,

On 30/08/17 11:20, Auger Eric wrote:
> 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.

Ah, fair enough. I guess del_consumer() does nothing on PCI?

Thanks,

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