> From: Alex Williamson <alex.williamson@xxxxxxxxxx> > Sent: Tuesday, March 28, 2023 11:18 PM > > On Tue, 28 Mar 2023 15:00:42 +0000 > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > Sent: Tuesday, March 28, 2023 10:46 PM > > > > > > On Tue, 28 Mar 2023 14:38:12 +0000 > > > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > > > > > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > > > Sent: Tuesday, March 28, 2023 10:26 PM > > > > > > > > > > On Tue, 28 Mar 2023 06:19:06 +0000 > > > > > "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > > > > > > > > > > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > > > > > > Sent: Tuesday, March 28, 2023 11:32 AM > > > > > > > > > > > > > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > > > > > > Sent: Tuesday, March 28, 2023 3:26 AM > > > > > > > > > > > > > > > > Additionally, VFIO_DEVICE_GET_PCI_HOT_RESET_INFO has a > flags > > > arg > > > > > that > > > > > > > > isn't used, why do we need a new ioctl vs defining > > > > > > > > VFIO_PCI_HOT_RESET_FLAG_IOMMUFD_DEV_ID. > > > > > > > > > > > > > > Sure. I can follow this suggestion. BTW. I have a doubt here. This > > > new > > > > > flag > > > > > > > is set by user. What if in the future kernel has new extensions and > > > needs > > > > > > > to report something new to the user and add new flags to tell > user? > > > Such > > > > > > > flag is set by kernel. Then the flags field may have two kinds of > flags > > > > > (some > > > > > > > set by user while some set by kernel). Will it mess up the flags > space? > > > > > > > > > > > > > > > > > > > flags in a GET_INFO ioctl is for output. > > > > > > > > > > > > if user needs to use flags as input to select different type of info > then it > > > > > should > > > > > > be split into multiple GET_INFO cmds. > > > > > > > > > > I don't know that that's actually a rule, however we don't currently > > > > > test flags is zero for input, so in this case I think we are stuck with > > > > > it only being for output. > > > > > > > > > > Alternatively, should VFIO_DEVICE_GET_PCI_HOT_RESET_INFO > > > > > automatically > > > > > return the dev_id variant of the output and set a flag to indicate this > > > > > is the case when called on a device fd opened as a cdev? Thanks, > > > > > > > > Personally I prefer that user asks for dev_id info explicitly. The major > > > reason > > > > that we return dev_id is that the group/bdf info is not enough for the > > > device > > > > fd passing case. But if qemu opens device by itself, the group/bdf info > is > > > still > > > > enough. So a device opened as a cdev doesn't mean it should return > > > dev_id, > > > > it depends on if user has the bdf knowledge. > > > > > > But if QEMU opens the cdev, vs getting it from the group, does it make > > > any sense to return a set of group-ids + bdf in the host-reset info? > > > I'm inclined to think the answer is no. > > > > > > Per my previous suggestion, I think we should always return the bdf. We > > > can't know if the user is accessing through an fd they opened > > > themselves or were passed, > > > > Oh, yes. I'm convinced by this reason since only cdev mode supports > device fd > > passing. So I'll reuse the existing _INFO and let kernel set a flag to mark > the returned > > info is dev_id+bdf. > > > > A check. If the device that the _INFIO is invoked is opened via cdev, but > there > > are devices in the dev_set that are got via VFIO_GROUP_GET_DEVICE_FD, > should > > I fail it or allow it? > > It's a niche case, but I think it needs to be allowed. I'm also wondering if it is common in the future. Actually, a user should be preferred to either use the group or cdev, but not both. Otherwise, it looks to be bad programming.:-) Also, as an earlier remark from Jason. If there are affected devices that are opened by other users, the new _INFO should fail with -EPERM. I know this remark was for the new _INFO ioctl. But now, we are going to reuse the existing _INFO, so I'd also want to check if we still need this policy? If yes, then it is a problem to check the owner of the devices that are opened by the group path. https://lore.kernel.org/kvm/ZBsF950laMs2ldFc@xxxxxxxxxx/ > We'd still > report the bdf for those devices, but make use of the invalid/null > dev-id. I think this empowers userspace that they could make the same > call on a group opened fd if necessary. For the devices opened via group path, it should have an entry that includes invalid_dev_id+bdf. So user can map it to the device. But there is no group_id, this may be fine since group is just a shortcut to find the device. Is it? > An alternative would be to > redefine the returned data structure entirely with a flag per entry > describing the output, but then I think we need to invent a kernel > policy of which gets reported, which seems overly complicated if our > goal is to phase out group usage. Make sense, or will this bite us? This does smell complicated. 😊 maybe minimum change is better as the group is going to be phased out. Regards, Yi Liu
