[PATCH v4 09/14] vfio/pci: Change vfio_pci_try_bus_reset() to use the dev_set

Jason Gunthorpe
2021-08-06T01:19:18Z

vfio_pci_try_bus_reset() is triggering a reset of the entire_dev set if
any device within it has accumulated a needs_reset. This reset can only be
done once all of the drivers operating the PCI devices to be reset are in
a known safe state.

Make this clearer by directly operating on the dev_set instead of the
vfio_pci_device. Rename the function to vfio_pci_dev_set_try_reset().

Use the device list inside the dev_set to check that all drivers are in a
safe state instead of working backwards from the pci_device.

The dev_set->lock directly prevents devices from joining/leaving the set,
or changing their state, which further implies the pci_device cannot
change drivers or that the vfio_device be freed, eliminating the need for
get/put's.

If a pci_device to be reset is not in the dev_set then the reset cannot be
used as we can't know what the state of that driver is. Directly measure
this by checking that every pci_device is in the dev_set - which
effectively proves that VFIO drivers are attached to everything.

Remove the odd interaction around vfio_pci_set_power_state() - have the
only caller avoid its redundant vfio_pci_set_power_state() instead of
avoiding it inside vfio_pci_dev_set_try_reset().

This restructuring corrects a call to pci_dev_driver() without holding the
device_lock() and removes a hard wiring to &vfio_pci_driver.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
drivers/vfio/pci/vfio_pci.c | 182 +++++++++++++++++-------------------
1 file changed, 86 insertions(+), 96 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 5d6db93d6c680f..0147f04c91b2fb 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 +2179,98 @@ 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;
+
+ list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
+ if (cur->dev == &pdev->dev)
+ return 0;
+ return -EBUSY;
+}
+
/*
- * If a bus or slot reset is available for the provided device and:
+ * 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.
+ *
+ * Returns the pci_dev to pass to pci_reset_bus() if every PCI device to be
+ * reset is inside the dev_set, and pci_reset_bus() can succeed. NULL otherwise.
+ */
+static struct pci_dev *
+vfio_pci_dev_set_resettable(struct vfio_device_set *dev_set)
+{
+ struct pci_dev *pdev;
+
+ lockdep_assert_held(&dev_set->lock);
+
+ /*
+ * 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;
+
+ /* pci_reset_bus() is supported */
+ if (pci_probe_reset_slot(pdev->slot) && pci_probe_reset_bus(pdev->bus))
+ return NULL;
+
+ if (vfio_pci_for_each_slot_or_bus(pdev, vfio_pci_is_device_in_set,
+ dev_set,
+ !pci_probe_reset_slot(pdev->slot)))
+ return NULL;
+ return pdev;
+}
+
+static bool vfio_pci_dev_set_needs_reset(struct vfio_device_set *dev_set)
+{
+ 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 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;
+ if (!vfio_pci_dev_set_needs_reset(dev_set))
+ return false;

- if (vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_count_devs,
- &i, slot) || !i)
- return;
+ pdev = vfio_pci_dev_set_resettable(dev_set);
+ if (!pdev)
+ return false;

- devs.max_index = i;
- devs.devices = kcalloc(i, sizeof(struct vfio_device *), GFP_KERNEL);
- if (!devs.devices)
- return;
+ ret = pci_reset_bus(pdev);
+ if (ret)
+ return false;

- if (vfio_pci_for_each_slot_or_bus(vdev->pdev,
- vfio_pci_get_unused_devs,
- &devs, slot))
- goto put_devs;
-
- /* 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;
- }
+ 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)
--
2.32.0