On Thu, 16 Jun 2022 17:18:16 +0300
Yishai Hadas <yishaih@xxxxxxxxxx> wrote:
> On 13/06/2022 10:13, Yishai Hadas wrote:
> > On 10/06/2022 6:32, Tian, Kevin wrote:
> >>> From: Yishai Hadas <yishaih@xxxxxxxxxx>
> >>> Sent: Monday, June 6, 2022 4:56 PM
> >>>
> >>> vfio core checks whether the driver sets some migration op (e.g.
> >>> set_state/get_state) and accordingly calls its op.
> >>>
> >>> However, currently mlx5 driver sets the above ops without regards to
> >>> its
> >>> migration caps.
> >>>
> >>> This might lead to unexpected usage/Oops if user space may call to the
> >>> above ops even if the driver doesn't support migration. As for example,
> >>> the migration state_mutex is not initialized in that case.
> >>>
> >>> The cleanest way to manage that seems to split the migration ops from
> >>> the main device ops, this will let the driver setting them separately
> >>> from the main ops when it's applicable.
> >>>
> >>> As part of that, changed HISI driver to match this scheme.
> >>>
> >>> This scheme may enable down the road to come with some extra group of
> >>> ops (e.g. DMA log) that can be set without regards to the other options
> >>> based on driver caps.
> >>>
> >>> Fixes: 6fadb021266d ("vfio/mlx5: Implement vfio_pci driver for mlx5
> >>> devices")
> >>> Signed-off-by: Yishai Hadas <yishaih@xxxxxxxxxx>
> >> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>, with one nit:
> >
> > Thanks Kevin, please see below.
> >
> >>
> >>> @@ -1534,8 +1534,8 @@ vfio_ioctl_device_feature_mig_device_state(struct
> >>> vfio_device *device,
> >>> struct file *filp = NULL;
> >>> int ret;
> >>>
> >>> - if (!device->ops->migration_set_state ||
> >>> - !device->ops->migration_get_state)
> >>> + if (!device->mig_ops->migration_set_state ||
> >>> + !device->mig_ops->migration_get_state)
> >>> return -ENOTTY;
> >> ...
> >>
> >>> @@ -1582,8 +1583,8 @@ static int
> >>> vfio_ioctl_device_feature_migration(struct vfio_device *device,
> >>> };
> >>> int ret;
> >>>
> >>> - if (!device->ops->migration_set_state ||
> >>> - !device->ops->migration_get_state)
> >>> + if (!device->mig_ops->migration_set_state ||
> >>> + !device->mig_ops->migration_get_state)
> >>> return -ENOTTY;
> >>>
> >> Above checks can be done once when the device is registered then
> >> here replaced with a single check on device->mig_ops.
> >>
> > I agree, it may look as of below.
> >
> > Theoretically, this could be done even before this patch upon device
> > registration.
> >
> > We could check that both 'ops' were set and *not* only one of and
> > later check for the specific 'op' upon the feature request.
> >
> > Alex,
> >
> > Do you prefer to switch to the below as part of V2 or stay as of
> > current submission and I'll just add Kevin as Reviewed-by ?
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_core.c
> > b/drivers/vfio/pci/vfio_pci_core.c
> > index a0d69ddaf90d..f42102a03851 100644
> > --- a/drivers/vfio/pci/vfio_pci_core.c
> > +++ b/drivers/vfio/pci/vfio_pci_core.c
> > @@ -1855,6 +1855,11 @@ int vfio_pci_core_register_device(struct
> > vfio_pci_core_device *vdev)
> > if (pdev->hdr_type != PCI_HEADER_TYPE_NORMAL)
> > return -EINVAL;
> >
> > + if (vdev->vdev.mig_ops &&
> > + !(vdev->vdev.mig_ops->migration_get_state &&
> > + vdev->vdev.mig_ops->migration_get_state))
> > + return -EINVAL;
> > +
> >
> > Yishai
> >
> Hi Alex,
>
> Did you have the chance to review the above note ?
>
> I would like to send V2 with Kevin's Reviewed-by tag for both patches,
> just wonder about the nit.
The whole mig_ops handling seems rather ad-hoc to me. What tells a
developer when mig_ops can be set? Can they be unset? Does this
enable a device feature callout to dynamically enable migration? Why do
we init the device with vfio_device_ops, but then open code per driver
setting vfio_migration_ops?
For the hisi_acc changes, they're specifically defining two device_ops,
one for migration and one without migration. This patch oddly makes
them identical other than the name and doesn't simplify the setup path,
which should now only require a single call point for init-device with
the proposed API rather than the existing three.
If we remove the migration callbacks from vfio_device_ops, there's also
an opportunity that we can fix the vfio_device_ops.name handling in
hisi_acc, where the only current user of this is to set the driver
override for spawned VFs from a vfio owned PF. This is probably
irrelevant for this driver, but clearly we have an expectation there
that name is the name of the module providing the ops and we have no
module named hisi-acc-vfio-pci-migration. Thanks,
Alex
