> From: Eric Auger <eric.auger@xxxxxxxxxx> > Sent: Tuesday, April 4, 2023 11:19 PM > > Hi Yi, > > On 4/4/23 16:37, Liu, Yi L wrote: > > Hi Eric, > > > >> From: Eric Auger <eric.auger@xxxxxxxxxx> > >> Sent: Tuesday, April 4, 2023 10:00 PM > >> > >> Hi YI, > >> > >> On 4/1/23 16:44, Yi Liu wrote: > >>> If the affected device is not opened by any user, it's safe to reset it > >>> given it's not in use. > >>> > >>> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx> > >>> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > >>> Tested-by: Yanting Jiang <yanting.jiang@xxxxxxxxx> > >>> Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx> > >>> --- > >>> drivers/vfio/pci/vfio_pci_core.c | 14 +++++++++++--- > >>> include/uapi/linux/vfio.h | 8 ++++++++ > >>> 2 files changed, 19 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > >>> index 65bbef562268..5d745c9abf05 100644 > >>> --- a/drivers/vfio/pci/vfio_pci_core.c > >>> +++ b/drivers/vfio/pci/vfio_pci_core.c > >>> @@ -2429,10 +2429,18 @@ static int vfio_pci_dev_set_hot_reset(struct > >> vfio_device_set *dev_set, > >>> list_for_each_entry(cur_vma, &dev_set->device_list, vdev.dev_set_list) { > >>> /* > >>> - * Test whether all the affected devices are contained by the > >>> - * set of groups provided by the user. > >>> + * Test whether all the affected devices can be reset by the > >>> + * user. > >>> + * > >>> + * Resetting an unused device (not opened) is safe, because > >>> + * dev_set->lock is held in hot reset path so this device > >>> + * cannot race being opened by another user simultaneously. > >>> + * > >>> + * Otherwise all opened devices in the dev_set must be > >>> + * contained by the set of groups provided by the user. > >>> */ > >>> - if (!vfio_dev_in_groups(cur_vma, groups)) { > >>> + if (cur_vma->vdev.open_count && > >>> + !vfio_dev_in_groups(cur_vma, groups)) { > >>> ret = -EINVAL; > >>> goto err_undo; > >>> } > >>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > >>> index 0552e8dcf0cb..f96e5689cffc 100644 > >>> --- a/include/uapi/linux/vfio.h > >>> +++ b/include/uapi/linux/vfio.h > >>> @@ -673,6 +673,14 @@ struct vfio_pci_hot_reset_info { > >>> * VFIO_DEVICE_PCI_HOT_RESET - _IOW(VFIO_TYPE, VFIO_BASE + 13, > >>> * struct vfio_pci_hot_reset) > >>> * > >>> + * Userspace requests hot reset for the devices it uses. Due to the > >>> + * underlying topology, multiple devices can be affected in the reset > >> by the reset > >>> + * while some might be opened by another user. To avoid interference > >> s/interference/hot reset failure? > > I don’t think user can really avoid hot reset failure since there may > > be new devices plugged into the affected slot. Even user has opened > I don't know the legacy wrt that issue but this sounds a serious issue, > meaning the reset of an assigned device could impact another device > belonging to another group not not owned by the user? but the hot reset shall fail as the group is not owned by the user. > > all the groups/devices reported by VFIO_DEVICE_GET_PCI_HOT_RESET_INFO, > > the hot reset can fail if new device is plugged in and has not been > > bound to vfio or opened by another user during the window of > > _INFO and HOT_RESET. > with respect to the latter isn't the dev_set lock held during the hot > reset and sufficient to prevent any new opening to occur? yes. new open needs to acquire the dev_set lock. So when hot reset acquires the dev_set lock, then no new open can occur. Regards, Yi Liu > > > > maybe the whole statement should be as below: > > > > To avoid interference, the hot reset can only be conducted when all > > the affected devices are either opened by the calling user or not > > opened yet at the moment of the hot reset attempt. > > OK > > Eric > > > >>> + * the calling user must ensure all affected devices, if opened, are > >>> + * owned by itself. > >>> + * > >>> + * The ownership is proved by an array of group fds. > >>> + * > >>> * Return: 0 on success, -errno on failure. > >>> */ > >>> struct vfio_pci_hot_reset { > > Regards, > > Yi Liu