Re: [PATCH v2 5/5] vfio/migration: Block VFIO migration with background snapshot

[Peter Xu]

On Thu, Aug 31, 2023 at 03:57:02PM +0300, Avihai Horon wrote:
> Background snapshot allows creating a snapshot of the VM while it's
> running and keeping it small by not including dirty RAM pages.
> 
> The way it works is by first stopping the VM, saving the non-iterable
> devices' state and then starting the VM and saving the RAM while write
> protecting it with UFFD. The resulting snapshot represents the VM state
> at snapshot start.
> 
> VFIO migration is not compatible with background snapshot.
> First of all, VFIO device state is not even saved in background snapshot
> because only non-iterable device state is saved. But even if it was
> saved, after starting the VM, a VFIO device could dirty pages without it
> being detected by UFFD write protection. This would corrupt the
> snapshot, as the RAM in it would not represent the RAM at snapshot
> start.
> 
> To prevent this, block VFIO migration with background snapshot.
> 
> Signed-off-by: Avihai Horon <avihaih@nvidia.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu