[+cc liquidio, benet, fm10k maintainers:
The patch below will affect you if your driver calls
pci_sriov_set_totalvfs(dev, 0);
Previously that caused a subsequent pci_sriov_get_totalvfs() to return
the totalVFs value from the SR-IOV capability. After this patch, it will
return 0, which has implications for VF enablement via the sysfs
"sriov_numvfs" file.]
On Fri, May 25, 2018 at 09:02:23AM -0500, Bjorn Helgaas wrote:
> On Thu, May 24, 2018 at 06:20:15PM -0700, Jakub Kicinski wrote:
> > Hi Bjorn!
> >
> > On Thu, 24 May 2018 18:57:48 -0500, Bjorn Helgaas wrote:
> > > On Mon, Apr 02, 2018 at 03:46:52PM -0700, Jakub Kicinski wrote:
> > > > Some user space depends on enabling sriov_totalvfs number of VFs
> > > > to not fail, e.g.:
> > > >
> > > > $ cat .../sriov_totalvfs > .../sriov_numvfs
> > > >
> > > > For devices which VF support depends on loaded FW we have the
> > > > pci_sriov_{g,s}et_totalvfs() API. However, this API uses 0 as
> > > > a special "unset" value, meaning drivers can't limit sriov_totalvfs
> > > > to 0. Remove the special values completely and simply initialize
> > > > driver_max_VFs to total_VFs. Then always use driver_max_VFs.
> > > > Add a helper for drivers to reset the VF limit back to total.
> > >
> > > I still can't really make sense out of the changelog.
> > >
> > > I think part of the reason it's confusing is because there are two
> > > things going on:
> > >
> > > 1) You want this:
> > >
> > > pci_sriov_set_totalvfs(dev, 0);
> > > x = pci_sriov_get_totalvfs(dev)
> > >
> > > to return 0 instead of total_VFs. That seems to connect with
> > > your subject line. It means "sriov_totalvfs" in sysfs could be
> > > 0, but I don't know how that is useful (I'm sure it is; just
> > > educate me :))
> >
> > Let me just quote the bug report that got filed on our internal bug
> > tracker :)
> >
> > When testing Juju Openstack with Ubuntu 18.04, enabling SR-IOV causes
> > errors because Juju gets the sriov_totalvfs for SR-IOV-capable device
> > then tries to set that as the sriov_numvfs parameter.
> >
> > For SR-IOV incapable FW, the sriov_totalvfs parameter should be 0,
> > but it's set to max. When FW is switched to flower*, the correct
> > sriov_totalvfs value is presented.
> >
> > * flower is a project name
>
> From the point of view of the PCI core (which knows nothing about
> device firmware and relies on the architected config space described
> by the PCIe spec), this sounds like an erratum: with some firmware
> installed, the device is not capable of SR-IOV, but still advertises
> an SR-IOV capability with "TotalVFs > 0".
>
> Regardless of whether that's an erratum, we do allow PF drivers to use
> pci_sriov_set_totalvfs() to limit the number of VFs that may be
> enabled by writing to the PF's "sriov_numvfs" sysfs file.
>
> But the current implementation does not allow a PF driver to limit VFs
> to 0, and that does seem nonsensical.
>
> > My understanding is OpenStack uses sriov_totalvfs to determine how many
> > VFs can be enabled, looks like this is the code:
> >
> > http://git.openstack.org/cgit/openstack/charm-neutron-openvswitch/tree/hooks/neutron_ovs_utils.py#n464
> >
> > > 2) You're adding the pci_sriov_reset_totalvfs() interface. I'm not
> > > sure what you intend for this. Is *every* driver supposed to
> > > call it in .remove()? Could/should this be done in the core
> > > somehow instead of depending on every driver?
> >
> > Good question, I was just thinking yesterday we may want to call it
> > from the core, but I don't think it's strictly necessary nor always
> > sufficient (we may reload FW without re-probing).
> >
> > We have a device which supports different number of VFs based on the FW
> > loaded. Some legacy FWs does not inform the driver how many VFs it can
> > support, because it supports max. So the flow in our driver is this:
> >
> > load_fw(dev);
> > ...
> > max_vfs = ask_fw_for_max_vfs(dev);
> > if (max_vfs >= 0)
> > return pci_sriov_set_totalvfs(dev, max_vfs);
> > else /* FW didn't tell us, assume max */
> > return pci_sriov_reset_totalvfs(dev);
> >
> > We also reset the max on device remove, but that's not strictly
> > necessary.
> >
> > Other users of pci_sriov_set_totalvfs() always know the value to set
> > the total to (either always get it from FW or it's a constant).
> >
> > If you prefer we can work out the correct max for those legacy cases in
> > the driver as well, although it seemed cleaner to just ask the core,
> > since it already has total_VFs value handy :)
> >
> > > I'm also having a hard time connecting your user-space command example
> > > with the rest of this. Maybe it will make more sense to me tomorrow
> > > after some coffee.
> >
> > OpenStack assumes it will always be able to set sriov_numvfs to
> > sriov_totalvfs, see this 'if':
> >
> > http://git.openstack.org/cgit/openstack/charm-neutron-openvswitch/tree/hooks/neutron_ovs_utils.py#n512
>
> Thanks for educating me. I think there are two issues here that we
> can separate. I extracted the patch below for the first.
>
> The second is the question of resetting driver_max_VFs. I think we
> currently have a general issue in the core:
>
> - load PF driver 1
> - driver calls pci_sriov_set_totalvfs() to reduce driver_max_VFs
> - unload PF driver 1
> - load PF driver 2
>
> Now driver_max_VFs is still stuck at the lower value set by driver 1.
> I don't think that's the way this should work.
>
> I guess this is partly a consequence of setting driver_max_VFs in
> sriov_init(), which is called before driver attach and should only
> depend on hardware characteristics, so it is related to the patch
> below. But I think we should fix it in general, not just for
> netronome.
>
>
> commit 4a338bc6f94b9ad824ac944f5dfc249d6838719c
> Author: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> Date: Fri May 25 08:18:34 2018 -0500
>
> PCI/IOV: Allow PF drivers to limit total_VFs to 0
>
> Some SR-IOV PF drivers implement .sriov_configure(), which allows
> user-space to enable VFs by writing the desired number of VFs to the sysfs
> "sriov_numvfs" file (see sriov_numvfs_store()).
>
> The PCI core limits the number of VFs to the TotalVFs advertised by the
> device in its SR-IOV capability. The PF driver can limit the number of VFs
> to even fewer (it may have pre-allocated data structures or knowledge of
> device limitations) by calling pci_sriov_set_totalvfs(), but previously it
> could not limit the VFs to 0.
>
> Change pci_sriov_get_totalvfs() so it always respects the VF limit imposed
> by the PF driver, even if the limit is 0.
>
> This sequence:
>
> pci_sriov_set_totalvfs(dev, 0);
> x = pci_sriov_get_totalvfs(dev);
>
> previously set "x" to TotalVFs from the SR-IOV capability. Now it will set
> "x" to 0.
>
> Signed-off-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 192b82898a38..d0d73dbbd5ca 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -469,6 +469,7 @@ static int sriov_init(struct pci_dev *dev, int pos)
> iov->nres = nres;
> iov->ctrl = ctrl;
> iov->total_VFs = total;
> + iov->driver_max_VFs = total;
> pci_read_config_word(dev, pos + PCI_SRIOV_VF_DID, &iov->vf_device);
> iov->pgsz = pgsz;
> iov->self = dev;
> @@ -827,10 +828,7 @@ int pci_sriov_get_totalvfs(struct pci_dev *dev)
> if (!dev->is_physfn)
> return 0;
>
> - if (dev->sriov->driver_max_VFs)
> - return dev->sriov->driver_max_VFs;
> -
> - return dev->sriov->total_VFs;
> + return dev->sriov->driver_max_VFs;
> }
> EXPORT_SYMBOL_GPL(pci_sriov_get_totalvfs);
>
