On Tue, Jul 27, 2021 at 12:53:09PM -0600, Alex Williamson wrote: > On Tue, 27 Jul 2021 14:32:09 -0300 > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > > On Tue, Jul 27, 2021 at 08:04:16AM +0200, Cornelia Huck wrote: > > > On Mon, Jul 26 2021, Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > > > > > > > On Mon, 26 Jul 2021 20:09:06 -0300 > > > > Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > > > > > > > >> On Mon, Jul 26, 2021 at 07:07:04PM +0200, Cornelia Huck wrote: > > > >> > > > >> > But I wonder why nobody else implements this? Lack of surprise removal? > > > >> > > > >> The only implementation triggers an eventfd that seems to be the same > > > >> eventfd as the interrupt.. > > > >> > > > >> Do you know how this works in userspace? I'm surprised that the > > > >> interrupt eventfd can trigger an observation that the kernel driver > > > >> wants to be unplugged? > > > > > > > > I think we're talking about ccw, but I see QEMU registering separate > > > > eventfds for each of the 3 IRQ indexes and the mdev driver specifically > > > > triggering the req_trigger...? Thanks, > > > > > > > > Alex > > > > > > Exactly, ccw has a trigger for normal I/O interrupts, CRW (machine > > > checks), and this one. > > > > If it is a dedicated eventfd for 'device being removed' why is it in > > the CCW implementation and not core code? > > The CCW implementation (likewise the vfio-pci implementation) owns > the IRQ index address space and the decision to make this a signal > to userspace rather than perhaps some handling a device might be > able to do internally. The core code holds the vfio_device_get() so long as the FD is open. There is no way to pass the wait_for_completion without userspace closing the FD, so there isn't really much choice for the drivers to do beyond signal to userpace to close the FD?? > For instance an alternate vfio-pci implementation might zap all > mmaps, block all r/w access, and turn this into a surprise removal. This is nice, but wouldn't close the FD, so needs core changes anyhow.. > Another implementation might be more aggressive to sending SIGKILL > to the user process. We don't try to revoke FDs from the kernel, it is racy, dangerous and unreliable. > This was the thought behind why vfio-core triggers the driver > request callback with a counter, leaving the policy to the driver. IMHO subsystem policy does not belong in drivers. Down that road lies a mess for userspace. Jason
