Re: [RFC PATCH v2 1/3] vfio: Move the saving of the config space to the right place in VFIO migration

[Alex Williamson]

On Thu, 10 Dec 2020 10:21:21 +0800
Shenming Lu <lushenming@huawei.com> wrote:

> On 2020/12/10 2:34, Alex Williamson wrote:
> > On Wed, 9 Dec 2020 13:29:47 +0100
> > Cornelia Huck <cohuck@redhat.com> wrote:
> >   
> >> On Wed, 9 Dec 2020 16:09:17 +0800
> >> Shenming Lu <lushenming@huawei.com> wrote:
> >>  
> >>> On ARM64 the VFIO SET_IRQS ioctl is dependent on the VM interrupt
> >>> setup, if the restoring of the VFIO PCI device config space is
> >>> before the VGIC, an error might occur in the kernel.
> >>>
> >>> So we move the saving of the config space to the non-iterable
> >>> process, so that it will be called after the VGIC according to
> >>> their priorities.
> >>>
> >>> As for the possible dependence of the device specific migration
> >>> data on it's config space, we can let the vendor driver to
> >>> include any config info it needs in its own data stream.
> >>> (Should we note this in the header file linux-headers/linux/vfio.h?)    
> >>
> >> Given that the header is our primary source about how this interface
> >> should act, we need to properly document expectations about what will
> >> be saved/restored when there (well, in the source file in the kernel.)
> >> That goes in both directions: what a userspace must implement, and what
> >> a vendor driver can rely on.  
> 
> Yeah, in order to make the vendor driver and QEMU cooperate better, we might
> need to document some expectations about the data section in the migration
> region...
> >>
> >> [Related, but not a todo for you: I think we're still missing proper
> >> documentation of the whole migration feature.]  
> > 
> > Yes, we never saw anything past v1 of the documentation patch.  Thanks,
> >   
> 
> By the way, is there anything unproper with this patch? Wish your suggestion. 
> :-)

I'm really hoping for some feedback from Kirti, I understand the NVIDIA
vGPU driver to have some dependency on this.  Thanks,

Alex

> >>> Signed-off-by: Shenming Lu <lushenming@huawei.com>
> >>> ---
> >>>  hw/vfio/migration.c | 25 +++++++++++++++----------
> >>>  1 file changed, 15 insertions(+), 10 deletions(-)    
> > 
> > .
> >   
>