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Subject: Re: [pci PATCH v8 0/4] Add support for unmanaged SR-IOV

On Mon, Apr 23, 2018 at 8:21 AM, Don Dutile <ddutile@redhat.com> wrote:
> On 04/21/2018 04:34 PM, Bjorn Helgaas wrote:
>> On Fri, Apr 20, 2018 at 12:28:08PM -0400, Alexander Duyck wrote:
>>> This series is meant to add support for SR-IOV on devices when the VFs
>>> are
>>> not managed by the kernel. Examples of recent patches attempting to do
>>> this
>>> include:
>>> virto - https://patchwork.kernel.org/patch/10241225/
>>> pci-stub - https://patchwork.kernel.org/patch/10109935/
>>> vfio - https://patchwork.kernel.org/patch/10103353/
>>> uio - https://patchwork.kernel.org/patch/9974031/
>>> Since this is quickly blowing up into a multi-driver problem it is
>>> probably
>>> best to implement this solution as generically as possible.
>>> This series is an attempt to do that. What we do with this patch set is
>>> provide a generic framework to enable SR-IOV in the case that the PF
>>> driver
>>> doesn't support managing the VFs itself.
>>> I based my patch set originally on the patch by Mark Rustad but there
>>> isn't
>>> much left after going through and cleaning out the bits that were no
>>> longer
>>> needed, and after incorporating the feedback from David Miller. At this
>>> point
>>> the only items to be fully reused was his patch description which is now
>>> present in patch 3 of the set.
>>> This solution is limited in scope to just adding support for devices that
>>> provide no functionality for SR-IOV other than allocating the VFs by
>>> calling pci_enable_sriov. Previous sets had included patches for VFIO,
>>> but
>>> for now I am dropping that as the scope of that work is larger then I
>>> think I can take on at this time.
>>> v2: Reduced scope back to just virtio_pci and vfio-pci
>>>      Broke into 3 patch set from single patch
>>>      Changed autoprobe behavior to always set when num_vfs is set
>>> non-zero
>>> v3: Updated Documentation to clarify when sriov_unmanaged_autoprobe is
>>> used
>>>      Wrapped vfio_pci_sriov_configure to fix build errors w/o SR-IOV in
>>> kernel
>>> v4: Dropped vfio-pci patch
>>>      Added ena and nvme to drivers now using
>>> pci_sriov_configure_unmanaged
>>>      Dropped pci_disable_sriov call in virtio_pci to be consistent with
>>> ena
>>> v5: Dropped sriov_unmanaged_autoprobe and pci_sriov_conifgure_unmanaged
>>>      Added new patch that enables pci_sriov_configure_simple
>>>      Updated drivers to use pci_sriov_configure_simple
>>> v6: Defined pci_sriov_configure_simple as NULL when SR-IOV is not enabled
>>>      Updated drivers to drop "#ifdef" checks for IOV
>>>      Added pci-pf-stub as place for PF-only drivers to add support
>>> v7: Dropped pci_id table explanation from pci-pf-stub driver
>>>      Updated pci_sriov_configure_simple to drop need for err value
>>>      Fixed comment explaining why pci_sriov_configure_simple is NULL
>>> v8: Dropped virtio from the set, support to be added later after TC
>>> approval
>>> Cc: Mark Rustad <mark.d.rustad@intel.com>
>>> Cc: Maximilian Heyne <mheyne@amazon.de>
>>> Cc: Liang-Min Wang <liang-min.wang@intel.com>
>>> Cc: David Woodhouse <dwmw@amazon.co.uk>
>>> ---
>>> Alexander Duyck (4):
>>>        pci: Add pci_sriov_configure_simple for PFs that don't manage VF
>>> resources
>>>        ena: Migrate over to unmanaged SR-IOV support
>>>        nvme: Migrate over to unmanaged SR-IOV support
>>>        pci-pf-stub: Add PF driver stub for PFs that function only to
>>> enable VFs
>>>   drivers/net/ethernet/amazon/ena/ena_netdev.c |   28 -------------
>>>   drivers/nvme/host/pci.c                      |   20 ----------
>>>   drivers/pci/Kconfig                          |   12 ++++++
>>>   drivers/pci/Makefile                         |    2 +
>>>   drivers/pci/iov.c                            |   31 +++++++++++++++
>>>   drivers/pci/pci-pf-stub.c                    |   54
>>> ++++++++++++++++++++++++++
>>>   include/linux/pci.h                          |    3 +
>>>   include/linux/pci_ids.h                      |    2 +
>>>   8 files changed, 106 insertions(+), 46 deletions(-)
>>>   create mode 100644 drivers/pci/pci-pf-stub.c
>> I tentatively applied these to pci/virtualization-review.
>> The code changes look fine, but I want to flesh out the changelogs a
>> little bit before merging them.
>> For example, I'm not sure what you mean by "devices where the PF is
>> not capable of managing VF resources."
> I agree w/Bjorn's assessment of the changelog.
> The VF's are (minimally) assigned via the pf-stub driver, so they are
> 'managed by the kernel'.
> The security model is the same as the existing one, which was the issue we
> resolved in the previous set(s) of patches.
> I am hoping that something like vfio will be used to deal with the VF
> ownership
> and the reset mechanisms during assignement & de-assignment to 'guests'
> (qemu-kvm, DPDK, or whatever user-process),
> so the known, existing security model(s) is(are) maintained as well.
> If so, it'd be good to add such verbage somewhere (as 0/n is not kept in
> anything but possibly Bjorn's patchwork, or whatever patch mgmt tool he
> uses, and future reference would be good to have) say, an update to
> Documentation/PCI/pci-iov-howto.txt.
> So... the 'unmanaged SR-IOV' Subject, IMO, is not a valid Subject for the
> patch series any longer.
> No objections to the patch series, as Bjorn noted, just the commit
> log(s)/nomenclature of what is really being done.
> The expectation of VF enablement via the PF was born out of the fairly
> complicated, and unique PF vs VF drivers of the first implementations, which
> AlexD knows so well.  This "VFs act just like PFs without SRIOV
> capabilities" support is what this patch set enables with a much lighter
> configuration mechanism.
> So, maybe the patch set ought to be 'lightweight SRIOV enablement'.
> --dd

I'd be good with this being referred to as "lightweight SRIOV enablement".

The only reason why I was referring to it as "unmanaged" was because I
am used to drivers that use the PF MMIO registers to manage VF
resources and that doesn't exist in this model. Obviously this is all
still managed via the extended PCIe configuration though so there is
still some management taking place by the PCI subsystem in the kernel.


- Alex

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