On 2018.05.22 09:53:37 -0600, Alex Williamson wrote: > [Cc +GVT-g maintainers/lists] > > On Tue, 22 May 2018 10:13:46 +0200 > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > > On Fri, 18 May 2018 13:10:25 -0600 > > Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > > > > > When we create an mdev device, we check for duplicates against the > > > parent device and return -EEXIST if found, but the mdev device > > > namespace is global since we'll link all devices from the bus. We do > > > catch this later in sysfs_do_create_link_sd() to return -EEXIST, but > > > with it comes a kernel warning and stack trace for trying to create > > > duplicate sysfs links, which makes it an undesirable response. > > > > > > Therefore we should really be looking for duplicates across all mdev > > > parent devices, or as implemented here, against our mdev device list. > > > Using mdev_list to prevent duplicates means that we can remove > > > mdev_parent.lock, but in order not to serialize mdev device creation > > > and removal globally, we add mdev_device.active which allows UUIDs to > > > be reserved such that we can drop the mdev_list_lock before the mdev > > > device is fully in place. > > > > > > Two behavioral notes; first, mdev_parent.lock had the side-effect of > > > serializing mdev create and remove ops per parent device. This was > > > an implementation detail, not an intentional guarantee provided to > > > the mdev vendor drivers. Vendor drivers can trivially provide this > > > serialization internally if necessary. Second, review comments note > > > the new -EAGAIN behavior when the device, and in particular the remove > > > attribute, becomes visible in sysfs. If a remove is triggered prior > > > to completion of mdev_device_create() the user will see a -EAGAIN > > > error. While the errno is different, receiving an error during this > > > period is not, the previous implementation returned -ENODEV for the > > > same condition. Furthermore, the consistency to the user is improved > > > in the case where mdev_device_remove_ops() returns error. Previously > > > concurrent calls to mdev_device_remove() could see the device > > > disappear with -ENODEV and return in the case of error. Now a user > > > would see -EAGAIN while the device is in this transitory state. > > > > > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > --- > > > Documentation/vfio-mediated-device.txt | 5 ++ > > > drivers/vfio/mdev/mdev_core.c | 102 +++++++++++--------------------- > > > drivers/vfio/mdev/mdev_private.h | 2 - > > > 3 files changed, 42 insertions(+), 67 deletions(-) > > > > Reviewed-by: Cornelia Huck <cohuck@xxxxxxxxxx> > > > > I think it is better to deal with any possible vendor driver > > implications on top of this (I still believe that vfio-ccw is fine). > > Thanks Cornelia. So if vfio-ccw is fine, presumably NVIDIA is fine, > then this leaves GVT-g to see if there's any fallout. Zhenyu & Zhi, > I've linked the series under discussion here below[1]. The question to > you is the first of the two behavioral notes listed above, does GVT-g > have any dependency on the mdev core providing serialization per mdev > parent device for the create and remove callbacks within the > mdev_parent_ops? This was never an intended feature of the > implementation and as noted it should be trivial for for an mdev vendor > driver to provide equivalent course grained serialization if > necessary. Of course it would be better to implement that sooner > rather than later if required. > > I see that __intel_gvt_create_vgpu() makes use of gvt->lock, which > would seem to already provide this level of per-parent locking. The > remove path makes use of this same lock, so I think we're ok, but > looking for an explicit ack so there are no surprises. I'd like > to queue this series for v4.18. Thanks, > yeah, we don't expect mdev core for parent serialization for create and remove of mdev device. Series look good to me. Acked-by: Zhenyu Wang <zhenyuw@xxxxxxxxxxxxxxx> > Alex > > [1] https://lkml.org/lkml/2018/5/18/1035 -- Open Source Technology Center, Intel ltd. $gpg --keyserver wwwkeys.pgp.net --recv-keys 4D781827
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