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

[Chen Fan <chen.fan.fnst@cn.fujitsu.com>]

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.
Indeed, you're right, for subordinate buses reset, we should have a common
mechanism for all bridges.

>
>> 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,
it should be, let me try to think about it carefully.;)

Thanks,
Chen
>
> Alex
>
>
> .
>