On 9/29/2021 7:14 PM, Jason Gunthorpe wrote:

On Wed, Sep 29, 2021 at 06:28:44PM +0300, Max Gurtovoy wrote:

quoted

quoted

So you have a device that's actively modifying its internal state,
performing I/O, including DMA (thereby dirtying VM memory), all while
in the _STOP state?  And you don't see this as a problem?

I don't see how is it different from vfio-pci situation.

vfio-pci provides no way to observe the migration state. It isn't
"000b"

Alex said that there is a problem of compatibility.

I migration SW is not involved, nobody will read this migration state.

quoted

Maybe we need to rename STOP state. We can call it READY or LIVE or
NON_MIGRATION_STATE.

It was a poor choice to use 000b as stop, but it doesn't really
matter. The mlx5 driver should just pre-init this readable to running.

I guess we can do it for this reason. There is no functional problem nor 
compatibility issue here as was mentioned.

But still we need the kernel to track transitions. We don't want to 
allow moving from RESUMING to SAVING state for example. How this 
transition can be allowed ?

In this case we need to fail the request from the migration SW...

Jason