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

[Tan, Jianfeng]

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.y...@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