RE: [PATCH v1] vfio/common: Separate vfio-pci ranges

[Duan, Zhenzhong]

>-----Original Message-----
>From: Joao Martins <joao.m.martins@oracle.com>
>Sent: Monday, September 11, 2023 6:13 PM
>Subject: Re: [PATCH v1] vfio/common: Separate vfio-pci ranges
>
>On 11/09/2023 10:48, Duan, Zhenzhong wrote:
>>> -----Original Message-----
>>> From: Joao Martins <joao.m.martins@oracle.com>
>>> Sent: Monday, September 11, 2023 5:07 PM
>>> Subject: Re: [PATCH v1] vfio/common: Separate vfio-pci ranges
...
>> I have another question, previously I think vfio pci bars are device states 
>> and
>> save/restored through VFIO migration protocol, so we don't need to dirty
>> tracking them. Do I understand wrong?
>
>The general thinking of device dirty tracking is to track all addressable 
>IOVAs.
>But you do raise a good question. My understanding is that migrating the bars
>*as is* might be device migration specific (not a guarantee?); the save file 
>and
>precopy interface are the only places we transfer from/to the data and it's 
>just
>opaque data, not bars or anything formatted specifically -- so if we migrate
>bars it is hidden in what device f/w wants to move. Might be that BARs aren't
>even needed as they are sort of scratch space from h/w side. Ultimately, the
>dirty tracker is the one reporting the values, and the device h/w chooses to 
>not
>report those IOVAs as dirty then nothing changes.

Understood, thanks Joao.