netdev - Re: [PATCH V2 2/6] kvm: detect assigned device via irqbypass manager

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Message-ID: <f8e0ced4-2883-e022-8fd0-1224987ebef1@redhat.com>
Date:   Fri, 17 Jul 2020 12:01:29 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>, mst@...hat.com,
        alex.williamson@...hat.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH V2 2/6] kvm: detect assigned device via irqbypass manager


On 2020/7/16 下午7:23, Zhu Lingshan wrote:
> vDPA devices has dedicated backed hardware like
> passthrough-ed devices. Then it is possible to setup irq
> offloading to vCPU for vDPA devices. Thus this patch tries to
> manipulated assigned device counters via irqbypass manager.


This part needs some tweak, e.g why assigned device could be detected 
through this way.


>
> We will increase/decrease the assigned device counter in kvm/x86.


And you need explain why we don't need similar thing in other arch.

Thanks


> Both vDPA and VFIO would go through this code path.
>
> This code path only affect x86 for now.
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> Suggested-by: Jason Wang <jasowang@...hat.com>
> ---
>   arch/x86/kvm/x86.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 00c88c2..20c07d3 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10624,11 +10624,17 @@ int kvm_arch_irq_bypass_add_producer(struct irq_bypass_consumer *cons,
>   {
>   	struct kvm_kernel_irqfd *irqfd =
>   		container_of(cons, struct kvm_kernel_irqfd, consumer);
> +	int ret;
>   
>   	irqfd->producer = prod;
> +	kvm_arch_start_assignment(irqfd->kvm);
> +	ret = kvm_x86_ops.update_pi_irte(irqfd->kvm,
> +					 prod->irq, irqfd->gsi, 1);
> +
> +	if (ret)
> +		kvm_arch_end_assignment(irqfd->kvm);
>   
> -	return kvm_x86_ops.update_pi_irte(irqfd->kvm,
> -					   prod->irq, irqfd->gsi, 1);
> +	return ret;
>   }
>   
>   void kvm_arch_irq_bypass_del_producer(struct irq_bypass_consumer *cons,