On Thu, Nov 25 2021, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Thu, Nov 25, 2021 at 01:27:12PM +0100, Cornelia Huck wrote: >> On Wed, Nov 24 2021, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: >> >> > On Wed, Nov 24, 2021 at 05:55:49PM +0100, Cornelia Huck wrote: >> >> >> What I meant to say: If we give userspace the flexibility to operate >> >> this, we also must give different device types some flexibility. While >> >> subchannels will follow the general flow, they'll probably condense/omit >> >> some steps, as I/O is quite different to PCI there. >> > >> > I would say no - migration is general, no device type should get to >> > violate this spec. Did you have something specific in mind? There is >> > very little PCI specific here already >> >> I'm not really thinking about violating the spec, but more omitting >> things that do not really apply to the hardware. For example, it is >> really easy to shut up a subchannel, we don't really need to wait until >> nothing happens anymore, and it doesn't even have MMIO. > > I've never really looked closely at the s390 mdev drivers.. > > What does something like AP even do anyhow? The ioctl handler doesn't > do anything, there is no mmap hook, how does the VFIO userspace > interact with this thing? For AP, the magic is in the hardware/firmware; the vfio parts are needed to configure what is exposed to a given guest, not for operation. Once it is up, the hardware will handle any instructions directly, the hypervisor will not see them. (Unfortunately, none of the details have public documentation.) I have no idea how this would play with migration. > >> > In general, userspace can issue a VFIO_DEVICE_RESET ioctl and recover the >> > device back to device_state RUNNING. When a migration driver executes this >> > ioctl it should discard the data window and set migration_state to RUNNING as >> > part of resetting the device to a clean state. This must happen even if the >> > migration_state has errored. A freshly opened device FD should always be in >> > the RUNNING state. >> >> Can the state immediately change from RUNNING to ERROR again? > > Immediately? State change can only happen in response to the ioctl or > the reset. > > ""The migration_state cannot change asynchronously, upon writing the > migration_state the driver will either keep the current state and return > failure, return failure and go to ERROR, or succeed and go to the new state."" ok > >> > However, a device may not compromise system integrity if it is subjected to a >> > MMIO. It can not trigger an error TLP, it can not trigger a Machine Check, and >> > it can not compromise device isolation. >> >> "Machine Check" may be confusing to readers coming from s390; there, the >> device does not trigger the machine check, but the channel subsystem >> does, and we cannot prevent it. Maybe we can word it more as an example, >> so readers get an idea what the limits in this state are? > > Lets say x86 machine check then which is a kernel-fatal event. ok > >> Although I would like to see some more feedback from others, I think >> this is already a huge step in the right direction. > > Thanks, I made all your other changes > > Will send a v2 next week Thanks, sounds good.
