Re: [PATCH 1/4] PCI: introduce VFs reference counter and simplify pci_vfs_assigned() implementation

[Alex Williamson <alex.williamson@redhat.com>]

Since there's no 0th patch, I guess I'll comment here.  This series is
not bisectable, patch 1 breaks the existing implementation.  I'd
suggest:

patch 1 - fix i40e
patch 2 - create assign/deassign that uses dev_flags
patch 3 - convert users to new interface
patch 4 - convert interface to use atomic_t

IMHO, the assigned flag is a horrible hack and I don't know why drivers
like xenback need to use it.  KVM needs to use it because it doesn't
actually have a driver to bind to when a device is assigned, it's happy
to assign devices without any driver.  Thanks,

Alex


On Fri, 2014-07-11 at 08:47 +0800, Ethan Zhao wrote:
> Current implementation of helper function pci_vfs_assigned() is a little complex, to
> get sum of VFs that assigned to VM, access low level configuration space register and
> then loop in traversing device tree.
> 
> This patch introduce an atomic reference counter for VFs that assigned to VM in struct
> pci_sriov, and compose two more helper functions
> 
> pci_sriov_assign_device(),
> pci_sriov_deassign_device()
> 
> to replace manipulation to device flag and the meanwhile increase and decease the counter.
> 
> Passed building on 3.15.5
> 
> Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
> ---
>  drivers/pci/iov.c   |   65 ++++++++++++++++++++++++++++----------------------
>  drivers/pci/pci.h   |    1 +
>  include/linux/pci.h |    4 +++
>  3 files changed, 41 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index de7a747..72e267f 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -382,6 +382,7 @@ found:
>  	iov->nres = nres;
>  	iov->ctrl = ctrl;
>  	iov->total_VFs = total;
> +	atomic_set(&iov->VFs_assigned_cnt, 0);
>  	iov->offset = offset;
>  	iov->stride = stride;
>  	iov->pgsz = pgsz;
> @@ -603,45 +604,51 @@ 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
> + * pci_vfs_assigned - returns number of VFs are assigned to VM
> + * @dev: the physical PCI device that contains the VFs.
>   *
> - * Returns number of VFs belonging to this device that are assigned to a guest.
> + * Returns number of VFs belonging to this device that are assigned to VM.
>   * If device is not a physical function returns 0.
>   */
>  int pci_vfs_assigned(struct pci_dev *dev)
>  {
> -	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 0;
> +	if (dev->sriov)
> +		return atomic_read(&dev->sriov->VFs_assigned_cnt);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(pci_vfs_assigned);
>  
> -	/*
> -	 * 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);
> -	}
> +/**
> + * pci_sriov_assign_device - assign device to VM
> + * @pdev: the device to be assigned.
> + */
> +void pci_sriov_assign_device(struct pci_dev *pdev)
> +{
> +	pdev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
> +	if (pdev->is_virtfn && !pdev->is_physfn)
> +		if (pdev->physfn)
> +			if (pdev->physfn->sriov)
> +				atomic_inc(&pdev->physfn->sriov->
> +						VFs_assigned_cnt);
> +}
> +EXPORT_SYMBOL_GPL(pci_sriov_assign_device);
>  
> -	return vfs_assigned;
> +/**
> + * pci_sriov_deassign_device - deasign device from VM
> + * @pdev: the device to be deassigned.
> + */
> +void pci_sriov_deassign_device(struct pci_dev *pdev)
> +{
> +	pdev->dev_flags &= ~PCI_DEV_FLAGS_ASSIGNED;
> +	if (pdev->is_virtfn && !pdev->is_physfn)
> +		if (pdev->physfn)
> +			if (pdev->physfn->sriov)
> +				atomic_dec(&pdev->physfn->sriov->
> +						VFs_assigned_cnt);
>  }
> -EXPORT_SYMBOL_GPL(pci_vfs_assigned);
> +EXPORT_SYMBOL_GPL(pci_sriov_deassign_device);
>  
>  /**
>   * pci_sriov_set_totalvfs -- reduce the TotalVFs available
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 6bd0822..d17bda2 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -235,6 +235,7 @@ struct pci_sriov {
>  	u32 pgsz;		/* page size for BAR alignment */
>  	u8 link;		/* Function Dependency Link */
>  	u16 driver_max_VFs;	/* max num VFs driver supports */
> +	atomic_t VFs_assigned_cnt; /* counter of VFs assigned to VM */
>  	struct pci_dev *dev;	/* lowest numbered PF */
>  	struct pci_dev *self;	/* this PF */
>  	struct mutex lock;	/* lock for VF bus */
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index aab57b4..5cf6833 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1601,6 +1601,8 @@ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
>  void pci_disable_sriov(struct pci_dev *dev);
>  int pci_num_vf(struct pci_dev *dev);
>  int pci_vfs_assigned(struct pci_dev *dev);
> +void pci_sriov_assign_device(struct pci_dev *dev);
> +void pci_sriov_deassign_device(struct pci_dev *dev);
>  int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>  int pci_sriov_get_totalvfs(struct pci_dev *dev);
>  #else
> @@ -1610,6 +1612,8 @@ static inline void pci_disable_sriov(struct pci_dev *dev) { }
>  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 void pci_sriov_assign_device(struct pci_dev *dev) { }
> +static inline void pci_sriov_deassign_device(struct pci_dev *dev) { }
>  static inline int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs)
>  { return 0; }
>  static inline int pci_sriov_get_totalvfs(struct pci_dev *dev)