Re: [PATCH] virtio-pci: fix up config interrupt handling

[Cédric Le Goater]

On 1/9/22 18:49, Michael S. Tsirkin wrote:
> Fixes a couple of issues with irqfd use by config interrupt:
> - Rearrange initialization so cleanup happens in the reverse order
> - Don't use irqfd for config when not in use for data path
> I am not sure this is a complete fix though: I think we
> are better off limiting the effect to vdpa devices
> with config interrupt support. Or even bypass irqfd
> for config completely and inject into KVM using ioctl?
> The advantage would be less FDs used.
> This would mean mostly reverting the patchset though.
>
> Fixes: d5d24d859c ("virtio-pci: add support for configure interrupt")
> Cc: "Cindy Lu" <lulu@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

On a KVM guest with vhost, I am still seeing at reboot an issue :/

../hw/pci/msix.c:622: msix_unset_vector_notifiers: Assertion 
`dev->msix_vector_use_notifier && dev->msix_vector_release_notifier'


C.

> ---
>   hw/virtio/virtio-pci.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 98fb5493ae..b77cd69f97 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1130,15 +1130,15 @@ static int virtio_pci_set_guest_notifiers(DeviceState 
> *d, int nvqs, bool assign)
>               proxy->vector_irqfd =
>                   g_malloc0(sizeof(*proxy->vector_irqfd) *
>                             msix_nr_vectors_allocated(&proxy->pci_dev));
> +            r = kvm_virtio_pci_vector_config_use(proxy);
> +            if (r < 0) {
> +                goto config_error;
> +            }
>               r = kvm_virtio_pci_vector_use(proxy, nvqs);
>               if (r < 0) {
>                   goto config_assign_error;
>               }
>           }
> -        r = kvm_virtio_pci_vector_config_use(proxy);
> -        if (r < 0) {
> -            goto config_error;
> -        }
>           r = msix_set_vector_notifiers(&proxy->pci_dev, 
> virtio_pci_vector_unmask,
>                                         virtio_pci_vector_mask,
>                                         virtio_pci_vector_poll);
> @@ -1155,7 +1155,9 @@ notifiers_error:
>           kvm_virtio_pci_vector_release(proxy, nvqs);
>       }
>   config_error:
> -    kvm_virtio_pci_vector_config_release(proxy);
> +    if (with_irqfd) {
> +        kvm_virtio_pci_vector_config_release(proxy);
> +    }
>   config_assign_error:
>       virtio_pci_set_guest_notifier(d, VIRTIO_CONFIG_IRQ_IDX, !assign,
>                                     with_irqfd);