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

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 14, 2020 at 08:52:43AM +0800, Zhu, Lingshan wrote:
> 
> On 7/13/2020 6:52 PM, Michael S. Tsirkin wrote:
> 
>     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 <lingshan.zhu@intel.com>
> 
>             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.
> 
> Thanks Michael, so we should just drop changes in vfio, just increase / decrease
> the counter in irq bypass manager. right?
> 
> Thanks

I don't see any issue with that.

> 
> 
>                 ---
>                   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
>