Re: [PATCH 1/5] vfio/pci: Disable INTx fast path if using split irqchip

[Auger Eric]

Hi Peter,

On 2/26/20 11:50 PM, Peter Xu wrote:
> It's currently broken.  Let's use the slow path to at least make it
> functional.
> 
> Signed-off-by: Peter Xu <address@hidden>

> ---
>  hw/vfio/pci.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 5e75a95129..98e0e0c994 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -128,6 +128,18 @@ static void vfio_intx_enable_kvm(VFIOPCIDevice *vdev, 
> Error **errp)
>          return;
>      }
>  
> +    if (kvm_irqchip_is_split()) {
> +        /*
> +         * VFIO INTx is currently not working with split kernel
> +         * irqchip for level triggered interrupts.  Go the slow path
> +         * as long as split is enabled so we can be at least
> +         * functional (even with poor performance).
> +         *
> +         * TODO: Remove this after all things fixed up.
If this patch were to be applied sooner than the other patches as
suggested in the cover letter, We may emit a warning message saying that
slow path is selected due to split irqchip and this will induce perf
downgrade
> +         */
> +        return;
> +    }
> +
>      /* Get to a known interrupt state */
>      qemu_set_fd_handler(irqfd.fd, NULL, NULL, vdev);
>      vfio_mask_single_irqindex(&vdev->vbasedev, VFIO_PCI_INTX_IRQ_INDEX);
> 


Tested with a 5.2-rc1 kernel with reverted "654f1f13ea56  kvm: Check
irqchip mode before assign irqfd" and guest booting with nomsi.

Without this patch the assigned NIC does not work. This patch fixes the
issue.

Reviewed-by: Eric Auger <address@hidden>
Tested-by: Eric Auger <address@hidden>

Thanks

Eric