> -----Original Message----- > From: Jason Gunthorpe [mailto:jgg@xxxxxxxxxx] > Sent: 01 November 2021 17:25 > To: Alex Williamson <alex.williamson@xxxxxxxxxx>; Shameerali Kolothum > Thodi <shameerali.kolothum.thodi@xxxxxxxxxx> > Cc: Cornelia Huck <cohuck@xxxxxxxxxx>; Yishai Hadas <yishaih@xxxxxxxxxx>; > bhelgaas@xxxxxxxxxx; saeedm@xxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; > kvm@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; kuba@xxxxxxxxxx; > leonro@xxxxxxxxxx; kwankhede@xxxxxxxxxx; mgurtovoy@xxxxxxxxxx; > maorg@xxxxxxxxxx; Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx> > Subject: Re: [PATCH V2 mlx5-next 12/14] vfio/mlx5: Implement vfio_pci driver > for mlx5 devices > > On Fri, Oct 29, 2021 at 04:06:21PM -0600, Alex Williamson wrote: > > > > Right now we are focused on the non-P2P cases, which I think is a > > > reasonable starting limitation. > > > > It's a reasonable starting point iff we know that we need to support > > devices that cannot themselves support a quiescent state. Otherwise it > > would make sense to go back to work on the uAPI because I suspect the > > implications to userspace are not going to be as simple as "oops, can't > > migrate, there are two devices." As you say, there's a universe of > > devices that run together that don't care about p2p and QEMU will be > > pressured to support migration of those configurations. > > I agree with this, but I also think what I saw in the proposed hns > driver suggests it's HW cannot do quiescent, if so this is the first > counter-example to the notion it is a universal ability? > > hns people: Can you put your device in a state where it is operating, > able to accept and respond to MMIO, and yet guarentees it generates no > DMA transactions? AFAIK, I am afraid we cannot guarantee that as per our current implementation. At present in !RUNNING state we are putting the device in to a PAUSE state so it will complete the current request and keep the remaining ones in queue. But it can still receive a new request which will trigger the PAUSE state exit and resume the operation. So I guess, it is possible to corrupt the migration if user space misbehaves. Thanks, Shameer
