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

Christoffer Dall
2017-08-30T11:54:04Z

On Wed, Aug 30, 2017 at 10:59:46AM +0100, Marc Zyngier wrote:
> On 28/08/17 19:17, Christoffer Dall wrote:
> > 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?
>
> Hmm. I think that's a debug leftover from my early attempt at making
> things work with QEMU, which initializes things in the opposite order
> as kvmtool. It should be removed (or replaced by a fat WARN_ON).
>
> >> +
> >> + /*
> >> + * 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?
>
> Sure, will do.
>
> >
> >> + 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.
>
> Yes, makes sense.
>
> >> 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?
>
> Hey, for once I wasn't trying to optimize early! ;-) This would be
> useful indeed, as I expect GICv4 systems to be the absolute minority for
> the foreseeable future.
>

Right. For the record, I don't mind getting this functional first, and
adding the static key later, as you prefer.

Thanks,
-Christoffer