Re: [PATCH v3 09/14] vfio/pci: Change vfio_pci_try_bus_reset() to use the dev_set

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

On Thu, 5 Aug 2021 08:47:01 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Tue, Aug 03, 2021 at 10:52:25AM -0600, Alex Williamson wrote:
> > On Tue, 3 Aug 2021 13:41:52 -0300
> > Jason Gunthorpe <jgg@nvidia.com> wrote:  
> > > On Tue, Aug 03, 2021 at 10:34:06AM -0600, Alex Williamson wrote:  
> > > > I think the vfio_pci_find_reset_target() function needs to be re-worked
> > > > to just tell us true/false that it's ok to reset the provided device,
> > > > not to anoint an arbitrary target device.  Thanks,    
> > > 
> > > Yes, though this logic is confusing, why do we need to check if any
> > > device needs a reset at this point? If we are being asked to reset
> > > vdev shouldn't vdev needs_reset?
> > > 
> > > Or is the function more of a 'synchronize pending reset' kind of
> > > thing?  
> > 
> > Yes, the latter.  For instance think about a multi-function PCI device
> > such as a GPU.  The functions have dramatically different capabilities,
> > some might have function level reset abilities and others not.  We want
> > to be able to trigger a bus reset as the last device of the set is
> > released, no matter the order they're released and no matter the
> > capabilities of the device we're currently processing.  Thanks,  
> 
> I worked on this for awhile, I think this is much clearer about what
> this algorithm is trying to do:
> 
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index 5d6db93d6c680f..e418bcbb68facc 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -223,7 +223,7 @@ static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev)
>  	}
>  }
>  
> -static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev);
> +static bool vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set);
>  static void vfio_pci_disable(struct vfio_pci_device *vdev);
>  static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data);
>  
> @@ -404,6 +404,9 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
>  	struct vfio_pci_ioeventfd *ioeventfd, *ioeventfd_tmp;
>  	int i, bar;
>  
> +	/* For needs_reset */
> +	lockdep_assert_held(&vdev->vdev.dev_set->lock);
> +
>  	/* Stop the device from further DMA */
>  	pci_clear_master(pdev);
>  
> @@ -487,9 +490,7 @@ static void vfio_pci_disable(struct vfio_pci_device *vdev)
>  out:
>  	pci_disable_device(pdev);
>  
> -	vfio_pci_try_bus_reset(vdev);
> -
> -	if (!disable_idle_d3)
> +	if (!vfio_pci_dev_set_try_reset(vdev->vdev.dev_set) && !disable_idle_d3)
>  		vfio_pci_set_power_state(vdev, PCI_D3hot);
>  }
>  
> @@ -2145,36 +2146,6 @@ static struct pci_driver vfio_pci_driver = {
>  	.err_handler		= &vfio_err_handlers,
>  };
>  
> -static int vfio_pci_get_unused_devs(struct pci_dev *pdev, void *data)
> -{
> -	struct vfio_devices *devs = data;
> -	struct vfio_device *device;
> -	struct vfio_pci_device *vdev;
> -
> -	if (devs->cur_index == devs->max_index)
> -		return -ENOSPC;
> -
> -	device = vfio_device_get_from_dev(&pdev->dev);
> -	if (!device)
> -		return -EINVAL;
> -
> -	if (pci_dev_driver(pdev) != &vfio_pci_driver) {
> -		vfio_device_put(device);
> -		return -EBUSY;
> -	}
> -
> -	vdev = container_of(device, struct vfio_pci_device, vdev);
> -
> -	/* Fault if the device is not unused */
> -	if (device->open_count) {
> -		vfio_device_put(device);
> -		return -EBUSY;
> -	}
> -
> -	devs->devices[devs->cur_index++] = vdev;
> -	return 0;
> -}
> -
>  static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
>  {
>  	struct vfio_devices *devs = data;
> @@ -2208,79 +2179,86 @@ static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
>  	return 0;
>  }
>  
> +static int vfio_pci_is_device_in_set(struct pci_dev *pdev, void *data)
> +{
> +	struct vfio_device_set *dev_set = data;
> +	struct vfio_device *cur;
> +
> +	lockdep_assert_held(&dev_set->lock);
> +
> +	list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
> +		if (cur->dev == &pdev->dev)
> +			return 0;
> +	return -EBUSY;
> +}
> +
> +static bool vfio_pci_dev_set_needs_reset(struct vfio_device_set *dev_set)

Slight nit on the name here since we're essentially combining
needs_reset along with the notion of the device being unused.  I'm not
sure, maybe "should_reset"?  Otherwise it looks ok.  Thanks,

Alex

> +{
> +	struct vfio_pci_device *cur;
> +	bool needs_reset = false;
> +
> +	list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> +		/* No VFIO device in the set can have an open device FD */
> +		if (cur->vdev.open_count)
> +			return false;
> +		needs_reset |= cur->needs_reset;
> +	}
> +	return needs_reset;
> +}
> +
>  /*
> - * If a bus or slot reset is available for the provided device and:
> + * If a bus or slot reset is available for the provided dev_set and:
>   *  - All of the devices affected by that bus or slot reset are unused
> - *    (!refcnt)
>   *  - At least one of the affected devices is marked dirty via
>   *    needs_reset (such as by lack of FLR support)
> - * Then attempt to perform that bus or slot reset.  Callers are required
> - * to hold vdev->dev_set->lock, protecting the bus/slot reset group from
> - * concurrent opens.  A vfio_device reference is acquired for each device
> - * to prevent unbinds during the reset operation.
> - *
> - * NB: vfio-core considers a group to be viable even if some devices are
> - * bound to drivers like pci-stub or pcieport.  Here we require all devices
> - * to be bound to vfio_pci since that's the only way we can be sure they
> - * stay put.
> + * Then attempt to perform that bus or slot reset.
> + * Returns true if the dev_set was reset.
>   */
> -static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev)
> +static bool vfio_pci_dev_set_try_reset(struct vfio_device_set *dev_set)
>  {
> -	struct vfio_devices devs = { .cur_index = 0 };
> -	int i = 0, ret = -EINVAL;
> -	bool slot = false;
> -	struct vfio_pci_device *tmp;
> +	struct vfio_pci_device *cur;
> +	struct pci_dev *pdev;
> +	int ret;
>  
> -	if (!pci_probe_reset_slot(vdev->pdev->slot))
> -		slot = true;
> -	else if (pci_probe_reset_bus(vdev->pdev->bus))
> -		return;
> +	lockdep_assert_held(&dev_set->lock);
>  
> -	if (vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_count_devs,
> -					  &i, slot) || !i)
> -		return;
> +	/*
> +	 * By definition all PCI devices in the dev_set share the same PCI
> +	 * reset, so any pci_dev will have the same outcomes for
> +	 * pci_probe_reset_*() and pci_reset_bus().
> +	 */
> +	pdev = list_first_entry(&dev_set->device_list, struct vfio_pci_device,
> +				vdev.dev_set_list)->pdev;
>  
> -	devs.max_index = i;
> -	devs.devices = kcalloc(i, sizeof(struct vfio_device *), GFP_KERNEL);
> -	if (!devs.devices)
> -		return;
> +	/* Reset of the dev_set is possible */
> +	if (pci_probe_reset_slot(pdev->slot) && pci_probe_reset_bus(pdev->bus))
> +		return false;
>  
> -	if (vfio_pci_for_each_slot_or_bus(vdev->pdev,
> -					  vfio_pci_get_unused_devs,
> -					  &devs, slot))
> -		goto put_devs;
> +	if (!vfio_pci_dev_set_needs_reset(dev_set))
> +		return false;
>  
> -	/* Does at least one need a reset? */
> -	for (i = 0; i < devs.cur_index; i++) {
> -		tmp = devs.devices[i];
> -		if (tmp->needs_reset) {
> -			ret = pci_reset_bus(vdev->pdev);
> -			break;
> -		}
> +	/*
> +	 * vfio-core considers a group to be viable and will create a
> +	 * vfio_device even if some devices are bound to drivers like pci-stub
> +	 * or pcieport. Here we require all PCI devices to be inside our dev_set
> +	 * since that ensures they stay put and that every driver controlling
> +	 * the device can co-ordinate with the device reset.
> +	 */
> +	if (vfio_pci_for_each_slot_or_bus(pdev, vfio_pci_is_device_in_set,
> +					  dev_set,
> +					  !pci_probe_reset_slot(pdev->slot)))
> +		return false;
> +
> +	ret = pci_reset_bus(pdev);
> +	if (ret)
> +		return false;
> +
> +	list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
> +		cur->needs_reset = false;
> +		if (!disable_idle_d3)
> +			vfio_pci_set_power_state(cur, PCI_D3hot);
>  	}
> -
> -put_devs:
> -	for (i = 0; i < devs.cur_index; i++) {
> -		tmp = devs.devices[i];
> -
> -		/*
> -		 * If reset was successful, affected devices no longer need
> -		 * a reset and we should return all the collateral devices
> -		 * to low power.  If not successful, we either didn't reset
> -		 * the bus or timed out waiting for it, so let's not touch
> -		 * the power state.
> -		 */
> -		if (!ret) {
> -			tmp->needs_reset = false;
> -
> -			if (tmp != vdev && !disable_idle_d3)
> -				vfio_pci_set_power_state(tmp, PCI_D3hot);
> -		}
> -
> -		vfio_device_put(&tmp->vdev);
> -	}
> -
> -	kfree(devs.devices);
> +	return true;
>  }
>  
>  static void __exit vfio_pci_cleanup(void)
>