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Date: Tue, 11 Nov 2014 13:39:32 -0700
From: Alex Williamson <alex.williamson@...hat.com>
To: Don Dutile <ddutile@...hat.com>
Cc: Sathya Perla <sathya.perla@...lex.Com>, linux-pci@...r.kernel.org,
netdev@...r.kernel.org, ariel.elior@...gic.com,
linux.nics@...el.com, shahed.shaikh@...gic.com
Subject: Re: [PATCH 0/4] move pci_assivned_vfs() check (while disabling VFs)
to pci sub-system
On Tue, 2014-11-11 at 14:09 -0500, Don Dutile wrote:
> On 11/10/2014 06:53 AM, Sathya Perla wrote:
> > A user must not be allowed to disable VFs while they are already assigned to
> > a guest. This check is being made in each individual driver that implements
> > the sriov_configure PCI method.
> > This patch-set fixes this code duplication by moving this check from
> > drivers to the sriov_nuvfs_store() routine just before invoking
> > sriov_configure() when num_vfs is equal to 0.
> >
> > Vasundhara Volam (4):
> > pci: move pci_assivned_vfs() check while disabling VFs to pci
> > sub-system
> > bnx2x: remove pci_assigned_vfs() check while disabling VFs
> > i40e: remove pci_assigned_vfs() check while disabling VFs
> > qlcnic: remove pci_assigned_vfs() check while disabling VFs
> >
> > drivers/net/ethernet/broadcom/bnx2x/bnx2x_sriov.c | 2 +-
> > drivers/net/ethernet/intel/i40e/i40e_virtchnl_pf.c | 7 +------
> > .../net/ethernet/qlogic/qlcnic/qlcnic_sriov_pf.c | 10 ----------
> > drivers/pci/pci-sysfs.c | 5 +++++
> > 4 files changed, 7 insertions(+), 17 deletions(-)
> >
> I have had a side conversation with Alex Williamson, VFIO author.
>
> VFIO is the upstream method that device-assignment is managed/handled on kvm now.
> It does not set the PCI_DEV_FLAGS_ASSIGNED pci dev-flags, and thus,
> this check will not work when VFIO is used.
>
> This patch set will only work for the former, kvm-managed, device-assignment method,
> which is currently being deprecated in qemu as well.
>
> So, yes, it works for kvm managed device-assignment, but not the
> newer, VFIO-based device-assignment.
>
> Note, also, that the pci_assigned_vfs() check in the drivers will
> always return 0 when VFIO is used for device assignment, so keeping
> these checks in the drivers doesn't do what they imply either.
>
> So, taking in the patch solves old, kvm-managed, device assignment,
> but a new method is needed when VFIO is involved.
>
> - Don
>
> ps -- Note: just adding the flag setting in vfio-pci does not necessarily
> solve this problem. VFIO does not know if a device is assigned to a guest;
> it only knows a caller of the ioctl requesting the device to be assigned
> to vfio, and to be dma-mapped for a region of memory, has been requested.
> So, a new PF<->VF mechanism needs to be put in place to
> determine the equivalent information.
pps -- Note: testing pci_assivned_vfs() is racy, nothing prevents the flag
being added to a device between your check and removing the VF device.
This is one of the reasons that vfio-pci doesn't use it and that this
interface should be discouraged in the kernel.
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