RE: [PATCH v2 5/7] vfio/pci: Add sriov_configure support

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Alex Williamson
> Sent: Thursday, February 20, 2020 2:54 AM
> 
> With the VF Token interface we can now expect that a vfio userspace
> driver must be in collaboration with the PF driver, an unwitting
> userspace driver will not be able to get past the GET_DEVICE_FD step
> in accessing the device.  We can now move on to actually allowing
> SR-IOV to be enabled by vfio-pci on the PF.  Support for this is not
> enabled by default in this commit, but it does provide a module option
> for this to be enabled (enable_sriov=1).  Enabling VFs is rather
> straightforward, except we don't want to risk that a VF might get
> autoprobed and bound to other drivers, so a bus notifier is used to
> "capture" VFs to vfio-pci using the driver_override support.  We
> assume any later action to bind the device to other drivers is
> condoned by the system admin and allow it with a log warning.
> 
> vfio-pci will disable SR-IOV on a PF before releasing the device,
> allowing a VF driver to be assured other drivers cannot take over the
> PF and that any other userspace driver must know the shared VF token.
> This support also does not provide a mechanism for the PF userspace
> driver itself to manipulate SR-IOV through the vfio API.  With this
> patch SR-IOV can only be enabled via the host sysfs interface and the
> PF driver user cannot create or remove VFs.

I'm not sure how many devices can be properly configured simply 
with pci_enable_sriov. It is not unusual to require PF driver prepare
something before turning PCI SR-IOV capability. If you look kernel
PF drivers, there are only two using generic pci_sriov_configure_
simple (simple wrapper like pci_enable_sriov), while most others
implementing their own callback. However vfio itself has no idea
thus I'm not sure how an user knows whether using this option can
actually meet his purpose. I may miss something here, possibly 
using DPDK as an example will make it clearer.

> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>  drivers/vfio/pci/vfio_pci.c         |  106 +++++++++++++++++++++++++++++++--
> --
>  drivers/vfio/pci/vfio_pci_private.h |    2 +
>  2 files changed, 97 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index e4d5d26e5e71..b40ade48a844 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -54,6 +54,12 @@ module_param(disable_idle_d3, bool, S_IRUGO |
> S_IWUSR);
>  MODULE_PARM_DESC(disable_idle_d3,
>  		 "Disable using the PCI D3 low power state for idle, unused
> devices");
> 
> +static bool enable_sriov;
> +#ifdef CONFIG_PCI_IOV
> +module_param(enable_sriov, bool, 0644);
> +MODULE_PARM_DESC(enable_sriov, "Enable support for SR-IOV
> configuration");
> +#endif
> +
>  static inline bool vfio_vga_disabled(void)
>  {
>  #ifdef CONFIG_VFIO_PCI_VGA
> @@ -1528,6 +1534,35 @@ static const struct vfio_device_ops vfio_pci_ops =
> {
> 
>  static int vfio_pci_reflck_attach(struct vfio_pci_device *vdev);
>  static void vfio_pci_reflck_put(struct vfio_pci_reflck *reflck);
> +static struct pci_driver vfio_pci_driver;
> +
> +static int vfio_pci_bus_notifier(struct notifier_block *nb,
> +				 unsigned long action, void *data)
> +{
> +	struct vfio_pci_device *vdev = container_of(nb,
> +						    struct vfio_pci_device, nb);
> +	struct device *dev = data;
> +	struct pci_dev *pdev = to_pci_dev(dev);
> +	struct pci_dev *physfn = pci_physfn(pdev);
> +
> +	if (action == BUS_NOTIFY_ADD_DEVICE &&
> +	    pdev->is_virtfn && physfn == vdev->pdev) {
> +		pci_info(vdev->pdev, "Captured SR-IOV VF %s
> driver_override\n",
> +			 pci_name(pdev));
> +		pdev->driver_override = kasprintf(GFP_KERNEL, "%s",
> +						  vfio_pci_ops.name);
> +	} else if (action == BUS_NOTIFY_BOUND_DRIVER &&
> +		   pdev->is_virtfn && physfn == vdev->pdev) {
> +		struct pci_driver *drv = pci_dev_driver(pdev);
> +
> +		if (drv && drv != &vfio_pci_driver)
> +			pci_warn(vdev->pdev,
> +				 "VF %s bound to driver %s while PF bound to
> vfio-pci\n",
> +				 pci_name(pdev), drv->name);
> +	}
> +
> +	return 0;
> +}
> 
>  static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  {
> @@ -1539,12 +1574,12 @@ static int vfio_pci_probe(struct pci_dev *pdev,
> const struct pci_device_id *id)
>  		return -EINVAL;
> 
>  	/*
> -	 * Prevent binding to PFs with VFs enabled, this too easily allows
> -	 * userspace instance with VFs and PFs from the same device, which
> -	 * cannot work.  Disabling SR-IOV here would initiate removing the
> -	 * VFs, which would unbind the driver, which is prone to blocking
> -	 * if that VF is also in use by vfio-pci.  Just reject these PFs
> -	 * and let the user sort it out.
> +	 * Prevent binding to PFs with VFs enabled, the VFs might be in use
> +	 * by the host or other users.  We cannot capture the VFs if they
> +	 * already exist, nor can we track VF users.  Disabling SR-IOV here
> +	 * would initiate removing the VFs, which would unbind the driver,
> +	 * which is prone to blocking if that VF is also in use by vfio-pci.
> +	 * Just reject these PFs and let the user sort it out.
>  	 */
>  	if (pci_num_vf(pdev)) {
>  		pci_warn(pdev, "Cannot bind to PF with SR-IOV enabled\n");
> @@ -1592,6 +1627,18 @@ static int vfio_pci_probe(struct pci_dev *pdev,
> const struct pci_device_id *id)
>  			kfree(vdev);
>  			return -ENOMEM;
>  		}
> +
> +		vdev->nb.notifier_call = vfio_pci_bus_notifier;
> +		ret = bus_register_notifier(&pci_bus_type, &vdev->nb);
> +		if (ret) {
> +			kfree(vdev->vf_token);
> +			vfio_pci_reflck_put(vdev->reflck);
> +			vfio_del_group_dev(&pdev->dev);
> +			vfio_iommu_group_put(group, &pdev->dev);
> +			kfree(vdev);
> +			return ret;
> +		}
> +
>  		mutex_init(&vdev->vf_token->lock);
>  		uuid_gen(&vdev->vf_token->uuid);
>  	}
> @@ -1625,6 +1672,8 @@ static void vfio_pci_remove(struct pci_dev *pdev)
>  {
>  	struct vfio_pci_device *vdev;
> 
> +	pci_disable_sriov(pdev);
> +
>  	vdev = vfio_del_group_dev(&pdev->dev);
>  	if (!vdev)
>  		return;
> @@ -1635,6 +1684,9 @@ static void vfio_pci_remove(struct pci_dev *pdev)
>  		kfree(vdev->vf_token);
>  	}
> 
> +	if (vdev->nb.notifier_call)
> +		bus_unregister_notifier(&pci_bus_type, &vdev->nb);
> +
>  	vfio_pci_reflck_put(vdev->reflck);
> 
>  	vfio_iommu_group_put(pdev->dev.iommu_group, &pdev->dev);
> @@ -1683,16 +1735,48 @@ static pci_ers_result_t
> vfio_pci_aer_err_detected(struct pci_dev *pdev,
>  	return PCI_ERS_RESULT_CAN_RECOVER;
>  }
> 
> +static int vfio_pci_sriov_configure(struct pci_dev *pdev, int nr_virtfn)
> +{
> +	struct vfio_pci_device *vdev;
> +	struct vfio_device *device;
> +	int ret = 0;
> +
> +	might_sleep();
> +
> +	if (!enable_sriov)
> +		return -ENOENT;
> +
> +	device = vfio_device_get_from_dev(&pdev->dev);
> +	if (!device)
> +		return -ENODEV;
> +
> +	vdev = vfio_device_data(device);
> +	if (!vdev) {
> +		vfio_device_put(device);
> +		return -ENODEV;
> +	}
> +
> +	if (nr_virtfn == 0)
> +		pci_disable_sriov(pdev);
> +	else
> +		ret = pci_enable_sriov(pdev, nr_virtfn);
> +
> +	vfio_device_put(device);
> +
> +	return ret < 0 ? ret : nr_virtfn;
> +}
> +
>  static const struct pci_error_handlers vfio_err_handlers = {
>  	.error_detected = vfio_pci_aer_err_detected,
>  };
> 
>  static struct pci_driver vfio_pci_driver = {
> -	.name		= "vfio-pci",
> -	.id_table	= NULL, /* only dynamic ids */
> -	.probe		= vfio_pci_probe,
> -	.remove		= vfio_pci_remove,
> -	.err_handler	= &vfio_err_handlers,
> +	.name			= "vfio-pci",
> +	.id_table		= NULL, /* only dynamic ids */
> +	.probe			= vfio_pci_probe,
> +	.remove			= vfio_pci_remove,
> +	.sriov_configure	= vfio_pci_sriov_configure,
> +	.err_handler		= &vfio_err_handlers,
>  };
> 
>  static DEFINE_MUTEX(reflck_lock);
> diff --git a/drivers/vfio/pci/vfio_pci_private.h
> b/drivers/vfio/pci/vfio_pci_private.h
> index 76c11c915949..36ec69081ecd 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -13,6 +13,7 @@
>  #include <linux/irqbypass.h>
>  #include <linux/types.h>
>  #include <linux/uuid.h>
> +#include <linux/notifier.h>
> 
>  #ifndef VFIO_PCI_PRIVATE_H
>  #define VFIO_PCI_PRIVATE_H
> @@ -130,6 +131,7 @@ struct vfio_pci_device {
>  	struct mutex		ioeventfds_lock;
>  	struct list_head	ioeventfds_list;
>  	struct vfio_pci_vf_token	*vf_token;
> +	struct notifier_block	nb;
>  };
> 
>  #define is_intx(vdev) (vdev->irq_type == VFIO_PCI_INTX_IRQ_INDEX)