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

From: Christoffer Dall
Date: Thu Aug 31 2017 - 08:37:03 EST

On Thu, Aug 31, 2017 at 11:24:37AM +0100, Marc Zyngier wrote:
> On 30/08/17 20:59, Christoffer Dall wrote:
> > On Wed, Aug 30, 2017 at 01:53:30PM +0100, Marc Zyngier wrote:
> >> On 30/08/17 12:46, Christoffer Dall wrote:
> >>> On Wed, Aug 30, 2017 at 11:28:08AM +0100, 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@xxxxxxx>
> >>>>>> ---
> >>>>>> 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,
> >>>>
> >>>> This is just wrong. We cannot assume that the vcpu_id has anything to do
> >>>> with the vpe_idx. It happens to be the same thing now, but the two things
> >>>> should be clearly disconnected.
> >>>>
> >>>> I suggest the following (untested):
> >>>>
> >>>> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> >>>> index cf5d6e2de6b8..0146e004401a 100644
> >>>> --- a/virt/kvm/arm/vgic/vgic-v4.c
> >>>> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> >>>> @@ -251,13 +251,27 @@ static void dump_routing(int virq, struct kvm_kernel_irq_routing_entry *irq_entr
> >>>>
> >>>> }
> >>>>
> >>>> +static int vgic_v4_vcpu_to_index(struct its_vm *its_vm, struct kvm_vcpu *vcpu)
> >>>> +{
> >>>> + int i;
> >>>> +
> >>>> + for (i = 0; i < its_vm->nr_vpes; i++) {
> >>>> + struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> >>>> +
> >>>> + if (its_vm->vpes[i] == vpe)
> >>>> + return i;
> >>>> + }
> >>>> +
> >>>> + return -ENODEV;
> >>>> +}
> >>>> +
> >>>
> >>> Stupid question: Can we change the struct its_vlpi_map to contain a
> >>> vpe pointer or in stead of or in addition to the index?
> >>
> >> This is obviously the right solution, because the *index* of the VPE
> >> doesn't really matter for a map/unmap (it only matters for doorbell
> >> operations, and that's a very different code path).
> >>
> >> I came up with the following (untested, again), which is much more
> >> appealing:
> >>
> >> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> >> index b47097a3e4b4..0607541fcafc 100644
> >> --- a/drivers/irqchip/irq-gic-v3-its.c
> >> +++ b/drivers/irqchip/irq-gic-v3-its.c
> >> @@ -900,7 +900,7 @@ static void its_send_vmapti(struct its_device *dev, u32 id)
> >> struct its_vlpi_map *map = &dev->event_map.vlpi_maps[id];
> >> struct its_cmd_desc desc;
> >>
> >> - desc.its_vmapti_cmd.vpe = map->vm->vpes[map->vpe_idx];
> >> + desc.its_vmapti_cmd.vpe = map->vpe;
> >> desc.its_vmapti_cmd.dev = dev;
> >> desc.its_vmapti_cmd.virt_id = map->vintid;
> >> desc.its_vmapti_cmd.event_id = id;
> >> @@ -914,7 +914,7 @@ static void its_send_vmovi(struct its_device *dev, u32 id)
> >> struct its_vlpi_map *map = &dev->event_map.vlpi_maps[id];
> >> struct its_cmd_desc desc;
> >>
> >> - desc.its_vmovi_cmd.vpe = map->vm->vpes[map->vpe_idx];
> >> + desc.its_vmovi_cmd.vpe = map->vpe;
> >> desc.its_vmovi_cmd.dev = dev;
> >> desc.its_vmovi_cmd.event_id = id;
> >> desc.its_vmovi_cmd.db_enabled = map->db_enabled;
> >> diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
> >> index 52661b838821..58a4d89aa82c 100644
> >> --- a/include/linux/irqchip/arm-gic-v4.h
> >> +++ b/include/linux/irqchip/arm-gic-v4.h
> >> @@ -62,15 +62,15 @@ struct its_vpe {
> >> * irq_set_vcpu_affinity().
> >> *
> >> * @vm: Pointer to the GICv4 notion of a VM
> >> + * @vpe: Pointer to the GICv4 notion of a virtual CPU (VPE)
> >> * @vintid: Virtual LPI number
> >> * @db_enabled: Is the VPE doorbell to be generated?
> >> - * @vpe_idx: Index (0-based) of the VPE in this VM. Not the vpe_id!
> >> */
> >> struct its_vlpi_map {
> >> struct its_vm *vm;
> >> + struct its_vpe *vpe;
> >> u32 vintid;
> >> bool db_enabled;
> >> - u16 vpe_idx;
> >> };
> >>
> >> enum its_vcpu_info_cmd_type {
> >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> >> index d790d0c74b8b..6ba3d73e0f70 100644
> >> --- a/virt/kvm/arm/vgic/vgic-its.c
> >> +++ b/virt/kvm/arm/vgic/vgic-its.c
> >> @@ -715,7 +715,7 @@ static int vgic_its_cmd_handle_movi(struct kvm *kvm, struct vgic_its *its,
> >> if (ret)
> >> return ret;
> >>
> >> - map.vpe_idx = vcpu->vcpu_id;
> >> + map.vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> >>
> >> return its_map_vlpi(ite->irq->host_irq, &map);
> >> }
> >> @@ -1184,7 +1184,7 @@ static int vgic_its_cmd_handle_movall(struct kvm *kvm, struct vgic_its *its,
> >> struct its_vlpi_map map;
> >>
> >> if (!its_get_vlpi(irq->host_irq, &map)) {
> >> - map.vpe_idx = vcpu2->vcpu_id;
> >> + map.vpe = &vcpu2->arch.vgic_cpu.vgic_v3.its_vpe;
> >> its_map_vlpi(irq->host_irq, &map);
> >> }
> >> }
> >> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> >> index cf5d6e2de6b8..6ece88322013 100644
> >> --- a/virt/kvm/arm/vgic/vgic-v4.c
> >> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> >> @@ -288,9 +288,9 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
> >> */
> >> map = (struct its_vlpi_map) {
> >> .vm = &kvm->arch.vgic.its_vm,
> >> + .vpe = &irq->target_vcpu->arch.vgic_cpu.vgic_v3.its_vpe,
> >> .vintid = irq->intid,
> >> .db_enabled = true,
> >> - .vpe_idx = irq->target_vcpu->vcpu_id,
> >> };
> >>
> >> if (its_map_vlpi(virq, &map))
> >>
> >> Maybe I'll introduce a vcpu_to_vpe() helper, but it already looks much
> >> better to me...
> >>
> > Yes, indeed. Looks good to me as well.
> >
> > The only thing that makes me slightly nervous is the use of target_vcpu,
> > but I think we rely on it never being NULL for LPIs elsewhere in the
> > code, so we should be fine.
> Hmmm. Maybe not. When mapping an LPI, you can assign it to a collection
> that is not yet mapped to a redistributor, hence no target_vcpu.

Oh right, the local vcpu varible in ...handle_mapi is initialized to
NULL, bummer I missed that.

>
> But in this case, vgic_its_resolve_lpi() fails, and we just don't enter
> this code path. Annoyingly, this also shows that I do not handle MAPC at
> all in this code, which is pretty embarrassing (I rely on MAPC being
> done before MAPI/MAPTI).
>
> I'll address that in the next version.
>

Looking forward to it ;)

-Christoffer