netdev - Re: [PATCH 2/7] kvm/vfio: detect assigned device via irqbypass manager

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Date:   Sun, 12 Jul 2020 09:29:02 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Zhu Lingshan <lingshan.zhu@...el.com>
Cc:     mst@...hat.com, jasowang@...hat.com, pbonzini@...hat.com,
        sean.j.christopherson@...el.com, wanpengli@...cent.com,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, dan.daly@...el.com
Subject: Re: [PATCH 2/7] kvm/vfio: detect assigned device via irqbypass
 manager

On Sun, 12 Jul 2020 22:49:21 +0800
Zhu Lingshan <lingshan.zhu@...el.com> wrote:

> We used to detect assigned device via VFIO manipulated device
> conters. This is less flexible consider VFIO is not the only
> interface for assigned device. vDPA devices has dedicated
> backed hardware as well. So this patch tries to detect
> the assigned device via irqbypass manager.
> 
> We will increase/decrease the assigned device counter in kvm/x86.
> Both vDPA and VFIO would go through this code path.
> 
> This code path only affect x86 for now.

No it doesn't, it only adds VFIO support to x86, but it removes it from
architecture neutral code.  Also a VFIO device does not necessarily
make use of the irqbypass manager, this depends on platform support and
enablement of this feature.   Therefore, NAK.  Thanks,

Alex
 
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> ---
>  arch/x86/kvm/x86.c | 10 ++++++++--
>  virt/kvm/vfio.c    |  2 --
>  2 files changed, 8 insertions(+), 4 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,
> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
> index 8fcbc50..111da52 100644
> --- a/virt/kvm/vfio.c
> +++ b/virt/kvm/vfio.c
> @@ -226,7 +226,6 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  		list_add_tail(&kvg->node, &kv->group_list);
>  		kvg->vfio_group = vfio_group;
>  
> -		kvm_arch_start_assignment(dev->kvm);
>  
>  		mutex_unlock(&kv->lock);
>  
> @@ -254,7 +253,6 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>  				continue;
>  
>  			list_del(&kvg->node);
> -			kvm_arch_end_assignment(dev->kvm);
>  #ifdef CONFIG_SPAPR_TCE_IOMMU
>  			kvm_spapr_tce_release_vfio_group(dev->kvm,
>  							 kvg->vfio_group);