netdev - Re: [net-next 08/14] pci: Add SRIOV helper function to determine if VFs are assigned to guest

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Date:	Mon, 22 Apr 2013 14:09:04 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Cc:	David Miller <davem@...emloft.net>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	netdev <netdev@...r.kernel.org>, gospo@...hat.com,
	sassmann@...hat.com,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [net-next 08/14] pci: Add SRIOV helper function to determine if
 VFs are assigned to guest

On Sat, Apr 20, 2013 at 9:31 PM, Jeff Kirsher
<jeffrey.t.kirsher@...el.com> wrote:
> On Sat, 2013-04-20 at 02:49 -0700, Jeff Kirsher wrote:
>> From: Alexander Duyck <alexander.h.duyck@...el.com>
>>
>> This function is meant to add a helper function that will determine if a PF
>> has any VFs that are currently assigned to a guest.  We currently have been
>> implementing this function per driver, and going forward I would like to avoid
>> that by making this function generic and using this helper.
>>
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
>> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
>
> Adding linux-pci mailing list and Bjorn to the CC.
>
> Bjorn- David Miller needs a signoff by PCI maintainer.
>
>> ---
>>  drivers/pci/iov.c   | 41 +++++++++++++++++++++++++++++++++++++++++
>>  include/linux/pci.h |  5 +++++
>>  2 files changed, 46 insertions(+)
>>
>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>> index ee599f2..fd99720 100644
>> --- a/drivers/pci/iov.c
>> +++ b/drivers/pci/iov.c
>> @@ -729,6 +729,47 @@ int pci_num_vf(struct pci_dev *dev)
>>  EXPORT_SYMBOL_GPL(pci_num_vf);
>>
>>  /**
>> + * pci_vfs_assigned - returns number of VFs are assigned to a guest
>> + * @dev: the PCI device
>> + *
>> + * Returns number of VFs belonging to this device that are assigned to a guest.
>> + * If device is not a physical function returns -ENODEV.
>> + */
>> +int pci_vfs_assigned(struct pci_dev *dev)

I guess the idea here is to replace be_find_vfs(),
igb_vfs_are_assigned(), ixgbe_vfs_are_assigned(), etc.  It does seem
good to reduce duplicated code.

I'm trying to figure out why this is safe -- there's no explicit
synchronization between the iteration through PCI devices looking for
matching VFs and the device assignment/deassignment paths that set or
clear PCI_DEV_FLAGS_ASSIGNED, so on the face of it, it looks like
things could change between calling pci_vfs_assigned() and using the
result to make a decision.

Most of the calls would be in .remove() functions, so maybe there's
some sort of synchronization in that path that  makes this safe.

Bjorn

>> +{
>> +     struct pci_dev *vfdev;
>> +     unsigned int vfs_assigned = 0;
>> +     unsigned short dev_id;
>> +
>> +     /* only search if we are a PF */
>> +     if (!dev->is_physfn)
>> +             return -ENODEV;
>> +
>> +     /*
>> +      * determine the device ID for the VFs, the vendor ID will be the
>> +      * same as the PF so there is no need to check for that one
>> +      */
>> +     pci_read_config_word(dev, dev->sriov->pos + PCI_SRIOV_VF_DID, &dev_id);
>> +
>> +     /* loop through all the VFs to see if we own any that are assigned */
>> +     vfdev = pci_get_device(dev->vendor, dev_id, NULL);
>> +     while (vfdev) {
>> +             /*
>> +              * It is considered assigned if it is a virtual function with
>> +              * our dev as the physical function and the assigned bit is set
>> +              */
>> +             if (vfdev->is_virtfn && (vfdev->physfn == dev) &&
>> +                 (vfdev->dev_flags & PCI_DEV_FLAGS_ASSIGNED))
>> +                     vfs_assigned++;
>> +
>> +             vfdev = pci_get_device(dev->vendor, dev_id, vfdev);
>> +     }
>> +
>> +     return vfs_assigned;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_vfs_assigned);
>> +
>> +/**
>>   * pci_sriov_set_totalvfs -- reduce the TotalVFs available
>>   * @dev: the PCI PF device
>>   * @numvfs: number that should be used for TotalVFs supported
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 2461033a..03b4d3c 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -1643,6 +1643,7 @@ extern int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
>>  extern void pci_disable_sriov(struct pci_dev *dev);
>>  extern irqreturn_t pci_sriov_migration(struct pci_dev *dev);
>>  extern int pci_num_vf(struct pci_dev *dev);
>> +extern int pci_vfs_assigned(struct pci_dev *dev);
>>  extern int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>>  extern int pci_sriov_get_totalvfs(struct pci_dev *dev);
>>  #else
>> @@ -1661,6 +1662,10 @@ static inline int pci_num_vf(struct pci_dev *dev)
>>  {
>>       return 0;
>>  }
>> +static inline int pci_vfs_assigned(struct pci_dev *dev)
>> +{
>> +     return 0;
>> +}
>>  static inline int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs)
>>  {
>>       return 0;
>
>
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