Re: [PATCH v3 53/59] KVM: arm/arm64: GICv4: Hook vPE scheduling into vgic flush/sync

Christoffer Dall
2017-08-28T18:17:58Z

On Mon, Jul 31, 2017 at 06:26:31PM +0100, Marc Zyngier wrote:
> The redistributor needs to be told which vPE is about to be run,
> and tells us whether there is any pending VLPI on exit.
>
> Let's add the scheduling calls to the vgic flush/sync functions,
> allowing the VLPIs to be delivered to the guest.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> virt/kvm/arm/vgic/vgic-v4.c | 24 ++++++++++++++++++++++++
> virt/kvm/arm/vgic/vgic.c | 4 ++++
> virt/kvm/arm/vgic/vgic.h | 1 +
> 3 files changed, 29 insertions(+)
>
> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> index 50721c4e3da5..0a8deefbcf1c 100644
> --- a/virt/kvm/arm/vgic/vgic-v4.c
> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> @@ -119,6 +119,30 @@ void vgic_v4_teardown(struct kvm *kvm)
> its_vm->vpes = NULL;
> }
>
> +int vgic_v4_schedule(struct kvm_vcpu *vcpu, bool on)
> +{
> + int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> +
> + if (!vgic_is_v4_capable(vcpu->kvm) || !irq)
> + return 0;

why do we need to check the its_vpe.irq here? This check is certainly
not untuitive, as I don't understand what happened on a v4 capable
system that somehow failed. Is it because a specific VM is configured
to not use VLPIs, or?

> +
> + /*
> + * Before making the VPE resident, make sure the redistributor
> + * expects us here.
> + */
> + if (on) {
> + int err;
> +
> + err = irq_set_affinity(irq, cpumask_of(smp_processor_id()));

This is pretty unintuitive, and coming here without having read your
documentation may make people completely puzzled. Could we provide a
pointer to the documentation that explains how the vpe irq hooks this
all together?

> + if (err) {
> + kvm_err("failed irq_set_affinity IRQ%d (%d)\n", irq, err);
> + return err;
> + }
> + }
> +
> + return its_schedule_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe, on);
> +}
> +

I'd prefer this function be split into two and follow the vgic notation
of having a flush and a sync function.

> static struct vgic_its *vgic_get_its(struct kvm *kvm,
> struct kvm_kernel_irq_routing_entry *irq_entry)
> {
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index dfac894f6f03..9ab52108989d 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -721,6 +721,8 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> {
> struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>
> + WARN_ON(vgic_v4_schedule(vcpu, false));
> +

This is in the critical path, so would it be worth considering a static
key to cater for non-GICv4 systems here?

> /* An empty ap_list_head implies used_lrs == 0 */
> if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head))
> return;
> @@ -733,6 +735,8 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> /* Flush our emulation state into the GIC hardware before entering the guest. */
> void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
> {
> + WARN_ON(vgic_v4_schedule(vcpu, true));
> +
> /*
> * If there are no virtual interrupts active or pending for this
> * VCPU, then there is no work to do and we can bail out without
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index 1210bf4681dc..693b654acf4d 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -234,5 +234,6 @@ int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
> bool vgic_is_v4_capable(struct kvm *kvm);
> int vgic_v4_init(struct kvm *kvm);
> void vgic_v4_teardown(struct kvm *kvm);
> +int vgic_v4_schedule(struct kvm_vcpu *vcpu, bool on);
>
> #endif
> --
> 2.11.0
>
Functionally, this looks correct.

Thanks,
-Christoffer