Re: [Qemu-devel] [PATCH v16 11/14] vfio: introduce last reset sequence id

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

On Tue, 2016-01-12 at 10:43 +0800, Cao jin wrote:
> From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> 
> avoid multi-reset host bus, we introduce sequence id to secify which
> bus is resetting. and if one of the dependent devices has been do reset.
> the others should skip.
> 
> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> ---
>  hw/vfio/pci.c | 15 +++++++++++++++
>  hw/vfio/pci.h |  3 +++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index ff25c9b..da4815e 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -1914,6 +1914,8 @@ static int vfio_check_host_bus_reset(VFIOPCIDevice *vdev)
>      /* List all affected devices by bus reset */
>      devices = &info->devices[0];
>  
> +    vdev->single_depend_dev = (info->count == 1);
> +
>      /* Verify that we have all the groups required */
>      for (i = 0; i < info->count; i++) {
>          PCIHostDeviceAddress host;
> @@ -2249,6 +2251,7 @@ static int vfio_pci_hot_reset(VFIOPCIDevice *vdev, bool single)
>  
>      vfio_pci_pre_reset(vdev);
>      vdev->vbasedev.needs_reset = false;
> +    vdev->last_bus_reset_seqid = 0;
>  
>      ret = vfio_get_hot_reset_info(vdev, &info);
>      if (ret) {
> @@ -2310,6 +2313,7 @@ static int vfio_pci_hot_reset(VFIOPCIDevice *vdev, bool single)
>                  }
>                  vfio_pci_pre_reset(tmp);
>                  tmp->vbasedev.needs_reset = false;
> +                tmp->last_bus_reset_seqid = vdev->pdev.bus->reset_seqid;
>                  multi = true;
>                  break;
>              }
> @@ -3006,6 +3010,17 @@ static void vfio_pci_reset(DeviceState *dev)
>  
>      trace_vfio_pci_reset(vdev->vbasedev.name);
>  
> +    /* if need to do a hot reset */
> +    if (pdev->bus->in_reset) {
> +        if (vdev->last_bus_reset_seqid == pdev->bus->reset_seqid) {
> +            vdev->last_bus_reset_seqid = 0;
> +            return;

Why would we ever clear this?  You're assuming there will only ever be
one reset callback per device per bus reset.  But we really don't need
to make that assumption.

> +        } else if ((vdev->features & VFIO_FEATURE_ENABLE_AER)) {
> +            vfio_pci_hot_reset(vdev, vdev->single_depend_dev);
> +            return;
> +        }
> +    }
> +
>      vfio_pci_pre_reset(vdev);
>  
>      if (vdev->resetfn && !vdev->resetfn(vdev)) {
> diff --git a/hw/vfio/pci.h b/hw/vfio/pci.h
> index b385f07..728cbb8 100644
> --- a/hw/vfio/pci.h
> +++ b/hw/vfio/pci.h
> @@ -143,6 +143,9 @@ typedef struct VFIOPCIDevice {
>      bool no_kvm_msi;
>      bool no_kvm_msix;
>  
> +    bool single_depend_dev;
> +    uint32_t last_bus_reset_seqid;
> +
>      NotifierWithReturn hotplug_notifier;
>  } VFIOPCIDevice;
>