Re: [Qemu-devel] [PATCH 1/5] virtio-pci: use ioeventfd even when KVM is disabled

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

On Thu, Jun 15, 2017 at 05:38:09PM +0100, Stefan Hajnoczi wrote:
> Old kvm.ko versions only supported a tiny number of ioeventfds so
> virtio-pci avoids ioeventfds when kvm_has_many_ioeventfds() returns 0.
> 
> Do not check kvm_has_many_ioeventfds() when KVM is disabled since it
> always returns 0.  Since commit 8c56c1a592b5092d91da8d8943c17777d6462a6f
> ("memory: emulate ioeventfd") it has been possible to use ioeventfds in
> qtest or TCG mode.
> 
> This patch makes -device virtio-blk-pci,iothread=iothread0 work even
> when KVM is disabled.
> 
> I have tested that virtio-blk-pci works under TCG both with and without
> iothread.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Don't we need to check we are on a host that supports eventfd?

> ---
>  hw/virtio/virtio-pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index f9b7244..9f55476 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1740,7 +1740,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev, Error **errp)
>      bool pcie_port = pci_bus_is_express(pci_dev->bus) &&
>                       !pci_bus_is_root(pci_dev->bus);
>  
> -    if (!kvm_has_many_ioeventfds()) {
> +    if (kvm_enabled() && !kvm_has_many_ioeventfds()) {
>          proxy->flags &= ~VIRTIO_PCI_FLAG_USE_IOEVENTFD;
>      }
>  
> -- 
> 2.9.4