Re: [Qemu-devel] [PATCH v14 Resend 10/13] pci: add pci device pre-post reset callbacks for host bus reset

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Dec 24, 2015 at 01:10:25PM +0800, Chen Fan wrote:
> 
> On 12/22/2015 05:07 AM, Alex Williamson wrote:
> >On Fri, 2015-12-18 at 11:29 +0800, Chen Fan wrote:
> >>On 12/18/2015 04:31 AM, Alex Williamson wrote:
> >>>On Thu, 2015-12-17 at 09:41 +0800, Cao jin wrote:
> >>>>From: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >>>>
> >>>>Particularly, For vfio devices, Once need to recovery devices
> >>>>by bus reset such as AER, we always need to reset the host bus
> >>>>to recovery the devices under the bus, so we need to add pci
> >>>>device
> >>>>callbacks to specify to do host bus reset.
> >>>>
> >>>>Signed-off-by: Chen Fan <chen.fan.fnst@cn.fujitsu.com>
> >>>>Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> >>>>---
> >>>>   hw/pci/pci.c         | 18 ++++++++++++++++++
> >>>>   hw/pci/pci_bridge.c  |  9 +++++++++
> >>>>   hw/vfio/pci.c        | 26 ++++++++++++++++++++++++++
> >>>>   hw/vfio/pci.h        |  2 ++
> >>>>   include/hw/pci/pci.h |  7 +++++++
> >>>>   5 files changed, 62 insertions(+)
> >>>>
> >>>>diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> >>>>index f6ca6ef..64fa2cc 100644
> >>>>--- a/hw/pci/pci.c
> >>>>+++ b/hw/pci/pci.c
> >>>>@@ -247,6 +247,24 @@ static void pci_do_device_reset(PCIDevice
> >>>>*dev)
> >>>>       msix_reset(dev);
> >>>>   }
> >>>>+void pci_device_pre_reset(PCIBus *bus, PCIDevice *dev, void
> >>>>*unused)
> >>>>+{
> >>>>+    PCIDeviceClass *dc = PCI_DEVICE_GET_CLASS(dev);
> >>>>+
> >>>>+    if (dc->pre_reset) {
> >>>>+        dc->pre_reset(dev);
> >>>>+    }
> >>>>+}
> >>>>+
> >>>>+void pci_device_post_reset(PCIBus *bus, PCIDevice *dev, void
> >>>>*unused)
> >>>>+{
> >>>>+    PCIDeviceClass *dc = PCI_DEVICE_GET_CLASS(dev);
> >>>>+
> >>>>+    if (dc->post_reset) {
> >>>>+        dc->post_reset(dev);
> >>>>+    }
> >>>>+}
> >>>>+
> >>>>   /*
> >>>>    * This function is called on #RST and FLR.
> >>>>    * FLR if PCI_EXP_DEVCTL_BCR_FLR is set
> >>>>diff --git a/hw/pci/pci_bridge.c b/hw/pci/pci_bridge.c
> >>>>index 40c97b1..ddb76ab 100644
> >>>>--- a/hw/pci/pci_bridge.c
> >>>>+++ b/hw/pci/pci_bridge.c
> >>>>@@ -267,8 +267,17 @@ void pci_bridge_write_config(PCIDevice *d,
> >>>>       newctl = pci_get_word(d->config + PCI_BRIDGE_CONTROL);
> >>>>       if (~oldctl & newctl & PCI_BRIDGE_CTL_BUS_RESET) {
> >>>>+        /*
> >>>>+         * Notify all vfio-pci devices under the bus
> >>>>+         * should do physical bus reset.
> >>>>+         */
> >>>>+        PCIBus *sec_bus = pci_bridge_get_sec_bus(s);
> >>>>+        pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> >>>>+                            pci_device_pre_reset, NULL);
> >>>>           /* Trigger hot reset on 0->1 transition. */
> >>>>           qbus_reset_all(&s->sec_bus.qbus);
> >>>>+        pci_for_each_device(sec_bus, pci_bus_num(sec_bus),
> >>>>+                            pci_device_post_reset, NULL);
> >>>>       }
> >>>>   }
> >>>>diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >>>>index e17dc89..df32618 100644
> >>>>--- a/hw/vfio/pci.c
> >>>>+++ b/hw/vfio/pci.c
> >>>>@@ -39,6 +39,7 @@
> >>>>   static void vfio_disable_interrupts(VFIOPCIDevice *vdev);
> >>>>   static void vfio_mmap_set_enabled(VFIOPCIDevice *vdev, bool
> >>>>enabled);
> >>>>+static int vfio_pci_hot_reset(VFIOPCIDevice *vdev, bool single);
> >>>>   /*
> >>>>    * Disabling BAR mmaping can be slow, but toggling it around
> >>>>INTx
> >>>>can
> >>>>@@ -1888,6 +1889,8 @@ 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;
> >>>>@@ -2029,10 +2032,26 @@ static int
> >>>>vfio_check_bus_reset(NotifierWithReturn *n, void *opaque)
> >>>>       return vfio_check_host_bus_reset(vdev);
> >>>>   }
> >>>>+static void vfio_aer_pre_reset(PCIDevice *pdev)
> >>>>+{
> >>>>+    VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
> >>>>+
> >>>>+    vdev->aer_reset = true;
> >>>>+    vfio_pci_hot_reset(vdev, vdev->single_depend_dev);
> >>>>+}
> >>>Doesn't this lead to multiple host bus resets per guest bus reset
> >>>in
> >>>many cases?  It looks like we'll do it once per vfio-pci device,
> >>>even
> >>>if those devices are on the same host bus.  That's a 1 second
> >>>operation
> >>>per device.  Can we avoid that?  Maybe some sort of sequence ID
> >>>could
> >>>help a device figure out whether it's already been reset as part of
> >>>a
> >>>dependent device for this particular guest bus reset.  Thanks,
> >>That's right, I missed this case, but I don't understand the scenario
> >>how to
> >>use a sequence ID to mark the device if been reset. can you detail it
> >>?
> >I don't really have a concrete idea for a sequence ID, it was just a
> >thought that maybe if each bus reset had a sequence ID then devices
> >could know whether they've already been reset for that sequence ID.
> >  The basic problem we have is that reset callbacks are per device and
> >it's difficult to infer which individual resets are part of that bus
> >reset.  In fact, do we propagate resets correctly down secondary
> >bridges?  We're triggering off a VM write of the bridge control bus
> >reset bit triggering from 0->1 and we then call qbus_reset_all() on
> >that qbus, which I think is just going to call pci_bridge_reset() for
> >any other bridges, which doesn't do anything about resetting deeper
> >subordinate buses.  I think that means that if we had a root port with
> >a switch below it and endpoints below that, if the VM triggered a
> >secondary bus reset at the root port, the endpoints would never see it,
> >which is not how real hardware works.
> Hi Alex,
> 
>     After think over the subordinate case, I think the qbus_reset_all()
> should also reset the deeper endpoints. which recursive the qbus and qdev
> to reset all devices blow sec bus and bridge device independently.
> 
> MST's suggestion in another mail to add a hot reset callback for sec bus
> reset
> should be good to avoid the couple of pre_reset/post_reset callbacks.
> thanks:)
> 
> but for the multiple resets triggering on the same bus, I think the virtual
> bus-level
> callback do not guarantee the host bus reset only once for all dependent
> devices.
> because the host reset dependent devices may not on the same virtual bus.
> we allowed that the dependent devices address below the bus. so the devices
> still don't know the host bus is in reset. here I think we should have a
> host bus
> model bind to all the dependent devices. when devices do hot reset, we mark
> the bus in reset. then other dependent devices know the bus is reset. how
> about
> this?
> 
> Thanks,
> Chen


What does "below bus" mean here?
Below what?


> >
> >>additional, there was a mechanism to compute device whether need to
> >>be reset
> >>by hot reset. so I simply modify the code as the following:
> >>
> >>diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >>index a9bc67e..42774ca 100644
> >>--- a/hw/vfio/pci.c
> >>+++ b/hw/vfio/pci.c
> >>@@ -2063,13 +2063,19 @@ static void vfio_aer_pre_reset(PCIDevice
> >>*pdev)
> >>       VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
> >>
> >>       vdev->aer_reset = true;
> >>-    vfio_pci_hot_reset(vdev, vdev->single_depend_dev);
> >>+    vdev->vbasedev.needs_reset = true;
> >>   }
> >>
> >>   static void vfio_aer_post_reset(PCIDevice *pdev)
> >>   {
> >>       VFIOPCIDevice *vdev = DO_UPCAST(VFIOPCIDevice, pdev, pdev);
> >>
> >>+    if (!vdev->single_depend_dev && vdev->vbasedev.needs_reset) {
> >>+        vfio_pci_hot_reset(vdev, false);
> >>+    } else {
> >>+        vfio_pci_hot_reset(vdev, true);
> >>+    }
> >>+
> >>       vdev->aer_reset = false;
> >>   }
> >>
> >>what do you think of this ?
> >I think it might be a bigger problem than that subtle change.  I wonder
> >if we really need a better model of the reset line through the
> >subordinate buses.  When reset is asserted, we'd set a bus_in_reset
> >flag on the bus and trigger downstream bridges to do the same.  Then
> >when the user de-asserts reset, we'd call qbus_reset_all() and
> >propagate it through to downstream buses.  That way the per device
> >reset callback could check to see if the bus is in reset and aer
> >devices can then know to do a bus reset.  Finally, the bus_in_reset
> >flag would be cleared on all the affected buses.  I'm sure there are
> >numerous details missing there, but it seems like it might be a
> >reasonable approach.  Thanks,
> >
> >Alex
> >
> >
> >.
> >
> 
>