Hi Marc,
Some feedback below, but mostly questions to aid my understanding...
On Tue, Sep 03, 2019 at 04:57:47PM +0100, Marc Zyngier wrote:
> When the VHE code was reworked, a lot of the vgic stuff was moved around,
> but the GICv4 residency code did stay untouched, meaning that we come
> in and out of residency on each flush/sync, which is obviously suboptimal.
>
> To address this, let's move things around a bit:
>
> - Residency entry (flush) moves to vcpu_load
> - Residency exit (sync) moves to vcpu_put
> - On blocking (entry to WFI), we "put"
> - On unblocking (exit from WFI, we "load"
>
> Because these can nest (load/block/put/load/unblock/put, for example),
> we now have per-VPE tracking of the residency state.
>
> Additionally, vgic_v4_put gains a "need doorbell" parameter, which only
> gets set to true when blocking because of a WFI. This allows a finer
> control of the doorbell, which now also gets disabled as soon as
> it gets signaled.
>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
> drivers/irqchip/irq-gic-v4.c | 7 +++-
> include/kvm/arm_vgic.h | 4 +--
> include/linux/irqchip/arm-gic-v4.h | 2 ++
> virt/kvm/arm/arm.c | 12 ++++---
> virt/kvm/arm/vgic/vgic-v3.c | 4 +++
> virt/kvm/arm/vgic/vgic-v4.c | 55 ++++++++++++++----------------
> virt/kvm/arm/vgic/vgic.c | 4 ---
> virt/kvm/arm/vgic/vgic.h | 2 --
> 8 files changed, 48 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v4.c b/drivers/irqchip/irq-gic-v4.c
> index 563e87ed0766..45969927cc81 100644
> --- a/drivers/irqchip/irq-gic-v4.c
> +++ b/drivers/irqchip/irq-gic-v4.c
> @@ -141,12 +141,17 @@ static int its_send_vpe_cmd(struct its_vpe *vpe, struct its_cmd_info *info)
> int its_schedule_vpe(struct its_vpe *vpe, bool on)
> {
> struct its_cmd_info info;
> + int ret;
>
> WARN_ON(preemptible());
>
> info.cmd_type = on ? SCHEDULE_VPE : DESCHEDULE_VPE;
>
> - return its_send_vpe_cmd(vpe, &info);
> + ret = its_send_vpe_cmd(vpe, &info);
> + if (!ret)
> + vpe->resident = on;
> +
We make an assumption here that its_schedule_vpe is the only caller of
its_send_vpe_cmd where we may pass SCHEDULE_VPE. I guess this is currently
the case.
Why do we also set the residency flag for DESCHEDULE_VPE?
And by residency we mean that interrupts are delivered to VM, instead of
doorbell?
> + return ret;
> }
>
> int its_invall_vpe(struct its_vpe *vpe)
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index af4f09c02bf1..4dc58d7a0010 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -396,7 +396,7 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int irq,
> int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
> struct kvm_kernel_irq_routing_entry *irq_entry);
>
> -void kvm_vgic_v4_enable_doorbell(struct kvm_vcpu *vcpu);
> -void kvm_vgic_v4_disable_doorbell(struct kvm_vcpu *vcpu);
> +int vgic_v4_load(struct kvm_vcpu *vcpu);
> +int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db);
>
> #endif /* __KVM_ARM_VGIC_H */
> diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
> index e6b155713b47..ab1396afe08a 100644
> --- a/include/linux/irqchip/arm-gic-v4.h
> +++ b/include/linux/irqchip/arm-gic-v4.h
> @@ -35,6 +35,8 @@ struct its_vpe {
> /* Doorbell interrupt */
> int irq;
> irq_hw_number_t vpe_db_lpi;
> + /* VPE resident */
> + bool resident;
> /* VPE proxy mapping */
> int vpe_proxy_event;
> /*
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index 35a069815baf..4e69268621b6 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -321,20 +321,24 @@ void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
> /*
> * If we're about to block (most likely because we've just hit a
> * WFI), we need to sync back the state of the GIC CPU interface
> - * so that we have the lastest PMR and group enables. This ensures
> + * so that we have the latest PMR and group enables. This ensures
> * that kvm_arch_vcpu_runnable has up-to-date data to decide
> * whether we have pending interrupts.
> + *
> + * For the same reason, we want to tell GICv4 that we need
> + * doorbells to be signalled, should an interrupt become pending.
As I understand, and as indicated by removal of kvm_vgic_v4_enable_doorbell
below, we've now abstracted enabling the doorbell behind the concept of a
v4_put.
Why then, do we break that abstraction by adding this comment? Surely we just
want to indicate that we're done with ITS for now - do whatever you need to do.
This would have made more sense to me if the comment above was removed in this
patch rather than added.
> */
> preempt_disable();
> kvm_vgic_vmcr_sync(vcpu);
> + vgic_v4_put(vcpu, true);
> preempt_enable();
> -
> - kvm_vgic_v4_enable_doorbell(vcpu);
> }
>
> void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
> {
> - kvm_vgic_v4_disable_doorbell(vcpu);
> + preempt_disable();
> + vgic_v4_load(vcpu);
> + preempt_enable();
> }
>
> int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index 8d69f007dd0c..48307a9eb1d8 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -664,6 +664,8 @@ void vgic_v3_load(struct kvm_vcpu *vcpu)
>
> if (has_vhe())
> __vgic_v3_activate_traps(vcpu);
> +
> + WARN_ON(vgic_v4_load(vcpu));
> }
>
> void vgic_v3_vmcr_sync(struct kvm_vcpu *vcpu)
> @@ -676,6 +678,8 @@ void vgic_v3_vmcr_sync(struct kvm_vcpu *vcpu)
>
> void vgic_v3_put(struct kvm_vcpu *vcpu)
> {
> + WARN_ON(vgic_v4_put(vcpu, false));
> +
> vgic_v3_vmcr_sync(vcpu);
>
> kvm_call_hyp(__vgic_v3_save_aprs, vcpu);
> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> index 477af6aebb97..3a8a28854b13 100644
> --- a/virt/kvm/arm/vgic/vgic-v4.c
> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> @@ -85,6 +85,10 @@ static irqreturn_t vgic_v4_doorbell_handler(int irq, void *info)
> {
> struct kvm_vcpu *vcpu = info;
>
> + /* We got the message, no need to fire again */
> + if (!irqd_irq_disabled(&irq_to_desc(irq)->irq_data))
> + disable_irq_nosync(irq);
> +
> vcpu->arch.vgic_cpu.vgic_v3.its_vpe.pending_last = true;
> kvm_make_request(KVM_REQ_IRQ_PENDING, vcpu);
> kvm_vcpu_kick(vcpu);
This is because the doorbell will fire each time any guest device interrupts,
however we only need to tell the guest just once that something has happened
right?
> @@ -192,20 +196,30 @@ void vgic_v4_teardown(struct kvm *kvm)
> its_vm->vpes = NULL;
> }
>
> -int vgic_v4_sync_hwstate(struct kvm_vcpu *vcpu)
> +int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db)
> {
> - if (!vgic_supports_direct_msis(vcpu->kvm))
> + struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> + struct irq_desc *desc = irq_to_desc(vpe->irq);
> +
> + if (!vgic_supports_direct_msis(vcpu->kvm) || !vpe->resident)
> return 0;
Are we using !vpe->resident to avoid pointlessly doing work we've
already done?
>
> - return its_schedule_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe, false);
> + /*
> + * If blocking, a doorbell is required. Undo the nested
> + * disable_irq() calls...
> + */
> + while (need_db && irqd_irq_disabled(&desc->irq_data))
> + enable_irq(vpe->irq);
> +
> + return its_schedule_vpe(vpe, false);
> }
>
> -int vgic_v4_flush_hwstate(struct kvm_vcpu *vcpu)
> +int vgic_v4_load(struct kvm_vcpu *vcpu)
> {
> - int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> + struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> int err;
>
> - if (!vgic_supports_direct_msis(vcpu->kvm))
> + if (!vgic_supports_direct_msis(vcpu->kvm) || vpe->resident)
> return 0;
>
> /*
> @@ -214,11 +228,14 @@ int vgic_v4_flush_hwstate(struct kvm_vcpu *vcpu)
> * doc in drivers/irqchip/irq-gic-v4.c to understand how this
> * turns into a VMOVP command at the ITS level.
> */
> - err = irq_set_affinity(irq, cpumask_of(smp_processor_id()));
> + err = irq_set_affinity(vpe->irq, cpumask_of(smp_processor_id()));
> if (err)
> return err;
>
> - err = its_schedule_vpe(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe, true);
> + /* Disabled the doorbell, as we're about to enter the guest */
> + disable_irq(vpe->irq);
> +
> + err = its_schedule_vpe(vpe, true);
> if (err)
> return err;
Given that the doorbell corresponds with vpe residency, it could make sense
to add a helper here that calls its_schedule_vpe and [disable,enable]_irq.
Though I see that vgic_v3_put calls vgic_v4_put with need_db=false. I wonder
what effect setting that to true would be for vgic_v3_put? Could it be known
that v3 won't set need_db to true?
Thanks,
Andrew Murray
>
> @@ -226,9 +243,7 @@ int vgic_v4_flush_hwstate(struct kvm_vcpu *vcpu)
> * Now that the VPE is resident, let's get rid of a potential
> * doorbell interrupt that would still be pending.
> */
> - err = irq_set_irqchip_state(irq, IRQCHIP_STATE_PENDING, false);
> -
> - return err;
> + return irq_set_irqchip_state(vpe->irq, IRQCHIP_STATE_PENDING, false);
> }
>
> static struct vgic_its *vgic_get_its(struct kvm *kvm,
> @@ -335,21 +350,3 @@ int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int virq,
> mutex_unlock(&its->its_lock);
> return ret;
> }
> -
> -void kvm_vgic_v4_enable_doorbell(struct kvm_vcpu *vcpu)
> -{
> - if (vgic_supports_direct_msis(vcpu->kvm)) {
> - int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> - if (irq)
> - enable_irq(irq);
> - }
> -}
> -
> -void kvm_vgic_v4_disable_doorbell(struct kvm_vcpu *vcpu)
> -{
> - if (vgic_supports_direct_msis(vcpu->kvm)) {
> - int irq = vcpu->arch.vgic_cpu.vgic_v3.its_vpe.irq;
> - if (irq)
> - disable_irq(irq);
> - }
> -}
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 45a870cb63f5..99b02ca730a8 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -857,8 +857,6 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
> {
> struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>
> - WARN_ON(vgic_v4_sync_hwstate(vcpu));
> -
> /* An empty ap_list_head implies used_lrs == 0 */
> if (list_empty(&vcpu->arch.vgic_cpu.ap_list_head))
> return;
> @@ -882,8 +880,6 @@ static inline void vgic_restore_state(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_flush_hwstate(vcpu));
> -
> /*
> * 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 83066a81b16a..c7fefd6b1c80 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -316,7 +316,5 @@ void vgic_its_invalidate_cache(struct kvm *kvm);
> bool vgic_supports_direct_msis(struct kvm *kvm);
> int vgic_v4_init(struct kvm *kvm);
> void vgic_v4_teardown(struct kvm *kvm);
> -int vgic_v4_sync_hwstate(struct kvm_vcpu *vcpu);
> -int vgic_v4_flush_hwstate(struct kvm_vcpu *vcpu);
>
> #endif
> --
> 2.20.1
>
