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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Mon, 13 Jul 2020 06:52:52 -0400

On Mon, Jul 13, 2020 at 04:13:35PM +0800, Jason Wang wrote:
> 
> On 2020/7/13 上午5:06, Michael S. Tsirkin wrote:
> > On Sun, Jul 12, 2020 at 10:49:21PM +0800, Zhu Lingshan 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.
> > > 
> > > Signed-off-by: Zhu Lingshan <[email-masked]>
> > 
> > I think it's best to leave VFIO alone. Add appropriate APIs for VDPA,
> > worry about converting existing users later.
> 
> 
> 
> Just to make sure I understand, did you mean:
> 
> 1) introduce another bridge for vDPA
> 
> or
> 
> 2) only detect vDPA via bypass manager? (we can leave VFIO code as is, then
> the assigned device counter may increase/decrease twice if VFIO use irq
> bypass manager which should be no harm).
> 
> Thanks

2 is probably easier to justify. 1 would depend on the specific bridge
proposed.

> 
> > 
> > > ---
> > >   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);
> > > -- 
> > > 1.8.3.1