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

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Date:   Mon, 28 Aug 2017 20:17:58 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Eric Auger <eric.auger@...hat.com>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: Re: [PATCH v3 53/59] KVM: arm/arm64: GICv4: Hook vPE scheduling into
 vgic flush/sync

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@....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