Re: [PATCH v6 1/1] vfio/qat: Add vfio_pci driver for Intel QAT SR-IOV VF devices

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Apr 24, 2024 at 03:34:19AM +0000, Zeng, Xin wrote:

> > > Like if it halts all queues and keeps them halted, while still
> > > allowing queue head/tail pointer updats then it would be a fine
> > > implementation for P2P.
> > 
> > Yes that really depends. e.g. a queue accepting direct stores (MOVDIR64B)
> > for work submission may have problem if that store is simply abandoned
> > when the queue is disabled. ENQCMD is possibly OK as unaccepted store
> > will get a retry indicator to software so nothing is lost.
> > 
> > I'll let Xin confirm on the QAT implementation (for all device registers).
> > If it is like Jason's example then we should provide a clear comment
> > clarifying that doing suspend at RUNNING_P2P is safe for QAT as the
> > device MMIO interface still works according to the definition of RUNNING
> > and no request is lost (either from CPU or peer). There is nothing to stop
> > from RUNNING_P2P to STOP because the device doesn't execute any
> > request to further change the internal state other than MMIO.
> > 
> 
> When QAT VF is suspended, all its MMIO registers can still be operated
> correctly, jobs submitted through ring are queued while no jobs are
> processed by the device.  The MMIO states can be safely migrated
> to the target VF during stop-copy stage and restored correctly in the
> target VF. All queued jobs can be resumed then. 
> MOVDIR64B mentioned above is not supported by QAT solution,
> so it's fine to keep current implementation.
> If no objections, I'll append this paragraph of comment in the driver and
> post another version.

Yes that looks good to me.

Jason