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

Alex Williamson
2021-08-05T17:33:22Z

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)
>