Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2011-11-29 at 13:01 +1100, Alexey Kardashevskiy wrote:
> Hi all,
> 
> Another problem I hit on POWER - MSI interrupts allocation. The existing VFIO does not expect a PBH
> to support less interrupts that a device might request. In my case, PHB's limit is 8 interrupts
> while my test card (10Gb ethernet CXGB3) wants 9. Below are the patches to demonstrate the idea.

Seems reasonable.  I assume we'd need similar for vfio_pci_setup_msi,
though I haven't seen anything use more than a single MSI interrupt.
Thanks,

Alex

> KERNEL patch:
> 
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 7d45c6b..d44b9bf 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -458,17 +458,32 @@ int vfio_pci_setup_msix(struct vfio_pci_device *vdev, int nvec, int __user *inta
>  		vdev->msix[i].entry = i;
>  		vdev->ev_msix[i] = ctx;
>  	}
> -	if (!ret)
> +	if (!ret) {
>  		ret = pci_enable_msix(pdev, vdev->msix, nvec);
> +		/*
> +		   The kernel is unable to allocate requested number of IRQs
> +		   and returned the available number.
> +		 */
> +		if (0 < ret) {
> +			ret = pci_enable_msix(pdev, vdev->msix, ret);
> +		}
> +	}
>  	vdev->msix_nvec = 0;
> -	for (i = 0; i < nvec && !ret; i++) {
> -		ret = request_irq(vdev->msix[i].vector, msihandler, 0,
> -				  "vfio", vdev->ev_msix[i]);
> -		if (ret)
> -			break;
> -		vdev->msix_nvec = i+1;
> +	if (0 == ret) {
> +		vdev->msix_nvec = 0;
> +		ret = 0;
> +		for (i = 0; i < nvec && !ret; i++) {
> +			ret = request_irq(vdev->msix[i].vector, msihandler, 0,
> +					"vfio", vdev->ev_msix[i]);
> +			if (ret)
> +				break;
> +			vdev->msix_nvec = i+1;
> +		}
> +		if ((0 == vdev->msix_nvec) && (0 != ret))
> +			vfio_pci_drop_msix(vdev);
> +		else
> +			ret = vdev->msix_nvec;
>  	}
> -	if (ret)
> -		vfio_pci_drop_msix(vdev);
> +
>  	return ret;
>  }
> 
> === end ===
> 
> 
> QEMU patch:
> 
> diff --git a/hw/vfio_pci.c b/hw/vfio_pci.c
> index 020961a..980eec7 100644
> --- a/hw/vfio_pci.c
> +++ b/hw/vfio_pci.c
> @@ -341,7 +341,8 @@ static void vfio_enable_msi(VFIODevice *vdev, bool msix)
>          }
>      }
> 
> -    if (ioctl(vdev->fd, VFIO_DEVICE_SET_IRQ_EVENTFDS, fds)) {
> +    ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQ_EVENTFDS, fds);
> +    if (0 > ret) {
>          fprintf(stderr, "vfio: Error: Failed to setup MSI/X fds %s\n",
>                  strerror(errno));
>          for (i = 0; i < vdev->nr_vectors; i++) {
> @@ -355,6 +356,8 @@ static void vfio_enable_msi(VFIODevice *vdev, bool msix)
>          qemu_free(vdev->msi_vectors);
>          vdev->nr_vectors = 0;
>          return;
> +    } else if (0 < ret) {
> +        vdev->nr_vectors = ret;
>      }
> 
>      vdev->interrupt = msix ? INT_MSIX : INT_MSI;
> 
> 
> === end ===