Re: [PATCH V5 17/25] vfio-pci: cpr part 2

[Zheng Chuan <zhengchuan@huawei.com>]

On 2021/7/30 20:52, Steven Sistare wrote:
> On 7/28/2021 12:56 AM, Zheng Chuan wrote:
>> On 2021/7/20 2:38, Steven Sistare wrote:
>>> On 7/19/2021 2:10 PM, Alex Williamson wrote:
>>>> On Mon, 19 Jul 2021 13:44:08 -0400
>>>> Steven Sistare <steven.sistare@oracle.com> wrote:
>>>>
>>>>> On 7/16/2021 4:51 PM, Alex Williamson wrote:
>>>>>> On Wed,  7 Jul 2021 10:20:26 -0700
>>>>>> Steve Sistare <steven.sistare@oracle.com> wrote:
>>>>>>   
>>>>>>> Finish cpr for vfio-pci by preserving eventfd's and vector state.
>>>>>>>
>>>>>>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>>>>>>> ---
>>>>>>>  hw/vfio/pci.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>>>>>>  1 file changed, 116 insertions(+), 2 deletions(-)
>>>>>>>
>>>>>>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>>>>>>> index 0f5c542..07bd360 100644
>>>>>>> --- a/hw/vfio/pci.c
>>>>>>> +++ b/hw/vfio/pci.c  
>>>>>> ...  
>>>>>>> @@ -3295,14 +3329,91 @@ static void vfio_merge_config(VFIOPCIDevice  
>>>>>> *vdev)  
>>>>>>>      g_free(phys_config);
>>>>>>>  }
>>>>>>>  
>>>>>>> +static int vfio_pci_pre_save(void *opaque)
>>>>>>> +{
>>>>>>> +    VFIOPCIDevice *vdev = opaque;
>>>>>>> +    PCIDevice *pdev = &vdev->pdev;
>>>>>>> +    int i;
>>>>>>> +
>>>>>>> +    if (vfio_pci_read_config(pdev, PCI_INTERRUPT_PIN, 1)) {
>>>>>>> +        error_report("%s: cpr does not support vfio-pci INTX",
>>>>>>> +                     vdev->vbasedev.name);
>>>>>>> +    }  
>>>>>>
>>>>>> You're not only not supporting INTx, but devices that support INTx, so
>>>>>> this only works on VFs.  Why?  Is this just out of scope or is there
>>>>>> something fundamentally difficult about it?
>>>>>>
>>>>>> This makes me suspect there's a gap in INTx routing setup if it's more
>>>>>> than just another eventfd to store and setup.  If we hot-add a device
>>>>>> using INTx after cpr restart, are we going to find problems?  Thanks,  
>>>>>
>>>>> It could be supported, but requires more code (several event fd's plus other state in VFIOINTx
>>>>> to save and restore) for a case that does not seem very useful (a directly assigned device that
>>>>> only supports INTx ?). 
>>>>
>>>> It's not testing that the device *only* supports INTx, it's testing
>>>> that the device supports INTx _at_all_.  That effectively means this
>>>> excludes anything other than an SR-IOV VF.  There are plenty of valid
>>>> and useful cases of assigning PFs, most of which support INTx even if
>>>> we don't expect that's their primary operational mode.  Thanks,
>>>
>>> OK, I'll look into it.  If this proves problematic, how do you feel about deferring
>>> INTx support to a later patch?
>>>
>> I am curious about that does cpr restart mode work for GPU passthrough?
> 
> It should work for any vfio device (after I fix the INTX limitation), but I have not tested
> a GPU yet.
> 
> - Steve
> .
Yes, The GPU may switch frequently between INTX and MSI, and cpr should support both of them:)
Thanks.
> 

-- 
Regards.
Chuan