linux-kernel - Re: [PATCH 09/10] KVM: arm/arm64: vgic: Implement forwarding setting

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Date:   Tue, 30 May 2017 16:03:15 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        alex.williamson@...hat.com, pbonzini@...hat.com,
        christoffer.dall@...aro.org, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH 09/10] KVM: arm/arm64: vgic: Implement forwarding setting

Hi Marc,

On 30/05/2017 15:17, Marc Zyngier wrote:
> On 30/05/17 13:54, Auger Eric wrote:
>> Hi,
>>
>> On 25/05/2017 21:19, Marc Zyngier wrote:
>>> On Wed, May 24 2017 at 10:13:22 pm BST, Eric Auger <eric.auger@...hat.com> wrote:
>>>> Implements kvm_vgic_[set|unset]_forwarding.
>>>>
>>>> Handle low-level VGIC programming and consistent irqchip
>>>> programming.
>>>>
>>>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>>>>
>>>> ---
>>>> ---
>>>>  include/kvm/arm_vgic.h   |   5 +++
>>>>  virt/kvm/arm/vgic/vgic.c | 105 +++++++++++++++++++++++++++++++++++++++++++++++
>>>>  2 files changed, 110 insertions(+)
>>>>
>>>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>>>> index 695ebc7..7ddac8a 100644
>>>> --- a/include/kvm/arm_vgic.h
>>>> +++ b/include/kvm/arm_vgic.h
>>>> @@ -343,4 +343,9 @@ int kvm_send_userspace_msi(struct kvm *kvm, struct kvm_msi *msi);
>>>>   */
>>>>  int kvm_vgic_setup_default_irq_routing(struct kvm *kvm);
>>>>  
>>>> +int kvm_vgic_set_forwarding(struct kvm *kvm, unsigned int irq,
>>>> +			    unsigned int virt_irq);
>>>> +void kvm_vgic_unset_forwarding(struct kvm *kvm, unsigned int irq,
>>>> +			       unsigned int virt_irq);
>>>
>>> nit: the name of the variables do not match that of the function
>>> definition, and are much clearer there.
>>>
>>>> +
>>>>  #endif /* __KVM_ARM_VGIC_H */
>>>> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
>>>> index aa0618c..c2add8d 100644
>>>> --- a/virt/kvm/arm/vgic/vgic.c
>>>> +++ b/virt/kvm/arm/vgic/vgic.c
>>>> @@ -17,6 +17,8 @@
>>>>  #include <linux/kvm.h>
>>>>  #include <linux/kvm_host.h>
>>>>  #include <linux/list_sort.h>
>>>> +#include <linux/interrupt.h>
>>>> +#include <linux/irq.h>
>>>>  
>>>>  #include "vgic.h"
>>>>  
>>>> @@ -771,3 +773,106 @@ bool kvm_vgic_map_is_active(struct kvm_vcpu *vcpu, unsigned int virt_irq)
>>>>  	return map_is_active;
>>>>  }
>>>>  
>>>> +/**
>>>> + * kvm_vgic_set_forwarding - Set IRQ forwarding
>>>> + *
>>>> + * @kvm: kvm handle
>>>> + * @host_irq: the host linux IRQ
>>>> + * @vintid: the virtual INTID
>>>> + *
>>>> + * This function must be called when the IRQ is not active:
>>>> + * ie. not active at GIC level and not currently under injection
>>>> + * into the guest using the unforwarded mode. The physical IRQ must
>>>> + * be disabled and all vCPUs must have been exited and prevented
>>>> + * from being re-entered.
>>>> + */
>>>> +int kvm_vgic_set_forwarding(struct kvm *kvm, unsigned int host_irq,
>>>> +			    unsigned int vintid)
>>>> +{
>>>> +	struct kvm_vcpu *vcpu;
>>>> +	struct vgic_irq *irq;
>>>> +	struct irq_desc *desc;
>>>> +	struct irq_data *data;
>>>> +	unsigned int pintid;
>>>> +	int ret = 0;
>>>> +
>>>> +
>>>> +	kvm_debug("%s host linux irq=%d vintid=%d\n",
>>>> +		  __func__, host_irq, vintid);
>>>> +
>>>> +	if (!vgic_valid_spi(kvm, vintid))
>>>> +		return 0;
>>>> +
>>>> +	/* find the INTID corresponding to @host_irq */
>>>> +	desc = irq_to_desc(host_irq);
>>>> +	if (!desc) {
>>>> +		kvm_err("%s: no interrupt descriptor\n", __func__);
>>>> +		return -EINVAL;
>>>> +	}
>>>> +
>>>> +	data = irq_desc_get_irq_data(desc);
>>>> +	while (data->parent_data)
>>>> +		data = data->parent_data;
>>>> +
>>>> +	pintid = data->hwirq;
>>>> +
>>>> +	irq = vgic_get_irq(kvm, NULL, vintid);
>>>> +
>>>> +	spin_lock(&irq->irq_lock);
>>>> +
>>>> +	vcpu = irq->target_vcpu;
>>>> +
>>>> +	if (!vcpu) {
>>>> +		ret = -EAGAIN;
>>>> +		goto unlock;
>>>> +	}
>>>> +
>>>> +	irq_set_vcpu_affinity(host_irq, vcpu);
>>>> +
>>>> +	irq->hw = true;
>>>> +	irq->hwintid = pintid;
>>>> +	irq->host_irq = host_irq;
>>>
>>> This feels like a duplication of kvm_vgic_map_phys_irq(), specially if
>>> you move the pintid discovery there. Can we somehow unify them?
>> Sure. At the beginning it was just a matter of irq_lock I did not want
>> to release.
>>
>> I was somehow embarrassed by the vcpu param of irq_set_vcpu_affinity.
>> Shall we really test target_vcpu. The actual value is unused for SPI so
>> shouldn't we simply use something != NULL.
> 
> I guess that for the time being, this would be good enough. But GICv4
> requires some actual tracking of the affinity, so we may have to bite
> the bullet already, and decide that the interrupt is always affine to a
> vcpu.
> 
> Does this have any userspace visible impact?
I don't see any.

Thanks

Eric
> 
> Thanks,
> 
> 	M.
>