Re: [dpdk-dev] [PATCH] net/virtio: fix use_msix get the wrong value

["Tan, Jianfeng" <jianfeng.tan@intel.com>]

On 10/31/2017 5:44 PM, Zhiyong Yang wrote:
> When running l3fwd-power to test virtio rxq interrupt using vfio
> pci noiommu mode, startup fails. In the function virtio_read_caps,
> the code if (flags & PCI_MSIX_ENABLE) intends to double check
> if vfio msix is enabled or not. However, it is indeed not valid.
> Come back to l3fwd-power, use_msix is not assigned to the right
> value "1". The patch fixes the issue.
>
> Fixes: cb482cb3a305 ("net/virtio: fix MAC address read")
> Signed-off-by: Zhiyong Yang <zhiyong.yang@intel.com>
> ---
>   drivers/net/virtio/virtio_pci.c | 11 +----------
>   1 file changed, 1 insertion(+), 10 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_pci.c b/drivers/net/virtio/virtio_pci.c
> index 55b717c03..be5b07a58 100644
> --- a/drivers/net/virtio/virtio_pci.c
> +++ b/drivers/net/virtio/virtio_pci.c
> @@ -580,8 +580,6 @@ get_cfg_addr(struct rte_pci_device *dev, struct virtio_pci_cap *cap)
>   	return base + offset;
>   }
>   
> -#define PCI_MSIX_ENABLE 0x8000
> -
>   static int
>   virtio_read_caps(struct rte_pci_device *dev, struct virtio_hw *hw)
>   {
> @@ -609,14 +607,7 @@ virtio_read_caps(struct rte_pci_device *dev, struct virtio_hw *hw)
>   		}
>   
>   		if (cap.cap_vndr == PCI_CAP_ID_MSIX) {
> -			/* Transitional devices would also have this capability,
> -			 * that's why we also check if msix is enabled.
> -			 * 1st byte is cap ID; 2nd byte is the position of next
> -			 * cap; next two bytes are the flags.
> -			 */
> -			uint16_t flags = ((uint16_t *)&cap)[1];
> -
> -			if (flags & PCI_MSIX_ENABLE)
> +			if (dev->intr_handle.type == RTE_INTR_HANDLE_VFIO_MSIX)
>   				hw->use_msix = 1;
>   		}
>   

The real issue is that, if vfio (noiommu) is used, msix enable 
(rte_intr_enable) is after the msix detection. IMO, we shall try to move 
msix enable ahead for virtio.
- igb_uio do that in the open().
- uio_pci_generic does not.
- vfio-pci does not.

For previous fix on mmio position adjustment, we might need to change to 
ask if msix is enabled each time.

Thanks,
Jianfeng