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. For instance an alternate vfio-pci implementation might zap all mmaps, block all r/w access, and turn this into a surprise removal. Another implementation might be more aggressive to sending SIGKILL to the user process. This was the thought behind why vfio-core triggers the driver request callback with a counter, leaving the policy to the driver. > Is PCI doing the same? Yes, that's where this handling originated. Thanks, Alex
