Re: [Qemu-devel] [PATCH v4 08/10] vfio: vote the function 0 to do host bus reset when aer occurred

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

On Tue, 22 Mar 2016 18:14:45 +0800
Chen Fan <chen.fan.fnst@cn.fujitsu.com> wrote:

> On 03/22/2016 05:40 AM, Alex Williamson wrote:
> > On Mon, 21 Mar 2016 18:08:44 +0800
> > Cao jin <caoj.fnst@cn.fujitsu.com> wrote:
> >  
> >> From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >>
> >> Due to all devices assigned to VM on the same way as host if enable
> >> aer, so we can easily do the hot reset by selecting the function #0
> >> to do the hot reset.
> >>
> >> Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >> ---
> >>   hw/vfio/pci.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >>   hw/vfio/pci.h |  2 ++
> >>   2 files changed, 52 insertions(+)
> >>
> >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >> index 9902c87..718cde7 100644
> >> --- a/hw/vfio/pci.c
> >> +++ b/hw/vfio/pci.c
> >> @@ -1900,6 +1900,8 @@ static void vfio_check_hot_bus_reset(VFIOPCIDevice *vdev, Error **errp)
> >>       /* 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;
> >> @@ -2608,11 +2610,36 @@ static void vfio_put_device(VFIOPCIDevice *vdev)
> >>   static void vfio_err_notifier_handler(void *opaque)
> >>   {
> >>       VFIOPCIDevice *vdev = opaque;
> >> +    PCIDevice *pdev = &vdev->pdev;
> >>   
> >>       if (!event_notifier_test_and_clear(&vdev->err_notifier)) {
> >>           return;
> >>       }
> >>   
> >> +    if (vdev->features & VFIO_FEATURE_ENABLE_AER) {
> >> +        VFIOPCIDevice *tmp;
> >> +        PCIDevice *dev;
> >> +        int devfn;
> >> +
> >> +        /*
> >> +         * If one device has aer capability on a bus, when aer occurred,
> >> +         * we should notify all devices on the bus there was an aer arrived,
> >> +         * then we are able to vote the device #0 to do host bus reset.
> >> +         */
> >> +        for (devfn = 0; devfn < 8; devfn++) {  
> > ARI?
> >  
> >> +            dev = pci_find_device(pdev->bus, pci_bus_num(pdev->bus),
> >> +                      PCI_DEVFN(PCI_SLOT(pdev->devfn), devfn));
> >> +            if (!dev) {
> >> +                continue;
> >> +            }
> >> +            if (!object_dynamic_cast(OBJECT(dev), "vfio-pci")) {
> >> +                continue;
> >> +            }
> >> +            tmp = DO_UPCAST(VFIOPCIDevice, pdev, dev);
> >> +            tmp->aer_occurred = true;
> >> +        }
> >> +    }
> >> +
> >>       /*
> >>        * TBD. Retrieve the error details and decide what action
> >>        * needs to be taken. One of the actions could be to pass
> >> @@ -3075,6 +3102,29 @@ static void vfio_pci_reset(DeviceState *dev)
> >>   
> >>       trace_vfio_pci_reset(vdev->vbasedev.name);
> >>   
> >> +    if (vdev->aer_occurred) {
> >> +        PCIDevice *br = pci_bridge_get_device(pdev->bus);
> >> +
> >> +        if (br &&
> >> +            (pci_get_word(br->config + PCI_BRIDGE_CONTROL) &
> >> +             PCI_BRIDGE_CTL_BUS_RESET)) {
> >> +            /* simply voting the function 0 to do hot bus reset */
> >> +            if (pci_get_function_0(pdev) == pdev) {
> >> +                if (vdev->features & VFIO_FEATURE_ENABLE_AER) {
> >> +                    vfio_pci_hot_reset(vdev, vdev->single_depend_dev);
> >> +                } else {
> >> +                    /* if this device has not AER capability, code
> >> +                     * coming here indicates there is another function
> >> +                     * on the bus has AER capability.
> >> +                     * */  
> > This shouldn't be possible, right?
> >  
> >> +                    vfio_pci_hot_reset(vdev, false);
> >> +                }
> >> +            }
> >> +            vdev->aer_occurred = false;
> >> +            return;
> >> +        }
> >> +    }  
> > Why do we care than an AER occurred now?  Can't we simply test:
> >
> >      if (vdev->features & VFIO_FEATURE_ENABLE_AER &&
> >          pci_get_function_0(pdev) == pdev) {
> >          PCIDevice *br = pci_bridge_get_device(pdev->bus);
> >
> >          if (pci_get_word(br->config + PCI_BRIDGE_CONTROL) &
> >              PCI_BRIDGE_CTL_BUS_RESET)) {
> >
> >              vfio_pci_hot_reset(vdev, vdev->single_depend_dev);
> >              return;
> >          }
> >      }  
> 
> do we have the case that only one/few of the devices affected
> by a bus reset assigned to VM enabled AER, then when bus
> reset, we let the function 0 do hot reset, which may not enable AER,
> but we should tell other devices on the bus that they don't need
> to do bus reset. so I just mark all devices on the bus when needing a 
> hot reset.

I thought we were requiring all the bus reset affected devices to
enable AER, so that example should not be possible.  I think it matches
our target use case to make this a requirement.  Thanks,

Alex