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


From: Steven Sistare
Subject: Re: [PATCH V5 17/25] vfio-pci: cpr part 2
Date: Fri, 30 Jul 2021 08:52:21 -0400
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0

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



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