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

Jason Gunthorpe
2021-07-29T00:50:04Z

Keep track of all the vfio_devices that have been added to the device set
and use this list in vfio_pci_try_bus_reset() instead of trying to work
backwards from the pci_device.

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

Completeness of the device set can be directly measured by checking if
every PCI device in the reset group is also in the device set - which
proves that VFIO drivers are attached to everything.

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 | 148 +++++++++++++++---------------------
1 file changed, 62 insertions(+), 86 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
index 5d6db93d6c680f..a1ae9a83a38621 100644
--- a/drivers/vfio/pci/vfio_pci.c
+++ b/drivers/vfio/pci/vfio_pci.c
@@ -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);

@@ -2145,7 +2148,7 @@ 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)
+static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
{
struct vfio_devices *devs = data;
struct vfio_device *device;
@@ -2165,8 +2168,11 @@ static int vfio_pci_get_unused_devs(struct pci_dev *pdev, void *data)

vdev = container_of(device, struct vfio_pci_device, vdev);

- /* Fault if the device is not unused */
- if (device->open_count) {
+ /*
+ * Locking multiple devices is prone to deadlock, runaway and
+ * unwind if we hit contention.
+ */
+ if (!vfio_pci_zap_and_vma_lock(vdev, true)) {
vfio_device_put(device);
return -EBUSY;
}
@@ -2175,112 +2181,82 @@ static int vfio_pci_get_unused_devs(struct pci_dev *pdev, void *data)
return 0;
}

-static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data)
+static int vfio_pci_is_device_in_set(struct pci_dev *pdev, void *data)
{
- struct vfio_devices *devs = data;
- struct vfio_device *device;
- struct vfio_pci_device *vdev;
+ struct vfio_device_set *dev_set = data;
+ struct vfio_device *cur;

- if (devs->cur_index == devs->max_index)
- return -ENOSPC;
+ lockdep_assert_held(&dev_set->lock);

- 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);
+ list_for_each_entry(cur, &dev_set->device_list, dev_set_list)
+ if (cur->dev == &pdev->dev)
+ return 0;
+ return -EBUSY;
+}

- /*
- * Locking multiple devices is prone to deadlock, runaway and
- * unwind if we hit contention.
- */
- if (!vfio_pci_zap_and_vma_lock(vdev, true)) {
- vfio_device_put(device);
- return -EBUSY;
+/*
+ * 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.
+ */
+static struct pci_dev *vfio_pci_find_reset_target(struct vfio_pci_device *vdev)
+{
+ struct vfio_device_set *dev_set = vdev->vdev.dev_set;
+ struct vfio_pci_device *cur;
+ bool needs_reset = false;
+
+ /* No VFIO device has an open device FD */
+ list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
+ if (cur->vdev.open_count)
+ return NULL;
+ needs_reset |= cur->needs_reset;
}
+ if (!needs_reset)
+ return NULL;

- devs->devices[devs->cur_index++] = vdev;
- return 0;
+ /* All PCI devices in the group to be reset need to be in our dev_set */
+ if (vfio_pci_for_each_slot_or_bus(
+ vdev->pdev, vfio_pci_is_device_in_set, dev_set,
+ !pci_probe_reset_slot(vdev->pdev->slot)))
+ return NULL;
+ return cur->pdev;
}

/*
* If a bus or slot reset is available for the provided device 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.
*/
static void vfio_pci_try_bus_reset(struct vfio_pci_device *vdev)
{
- struct vfio_devices devs = { .cur_index = 0 };
- int i = 0, ret = -EINVAL;
- bool slot = false;
- struct vfio_pci_device *tmp;
-
- if (!pci_probe_reset_slot(vdev->pdev->slot))
- slot = true;
- else if (pci_probe_reset_bus(vdev->pdev->bus))
- return;
+ struct vfio_device_set *dev_set = vdev->vdev.dev_set;
+ struct pci_dev *to_reset;
+ struct vfio_pci_device *cur;
+ int ret;

- if (vfio_pci_for_each_slot_or_bus(vdev->pdev, vfio_pci_count_devs,
- &i, slot) || !i)
- return;
+ lockdep_assert_held(&vdev->vdev.dev_set->lock);

- devs.max_index = i;
- devs.devices = kcalloc(i, sizeof(struct vfio_device *), GFP_KERNEL);
- if (!devs.devices)
+ if (pci_probe_reset_slot(vdev->pdev->slot) &&
+ pci_probe_reset_bus(vdev->pdev->bus))
return;

- 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;
- }
- }
-
-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;
+ to_reset = vfio_pci_find_reset_target(vdev);
+ if (!to_reset)
+ return;

- if (tmp != vdev && !disable_idle_d3)
- vfio_pci_set_power_state(tmp, PCI_D3hot);
- }
+ ret = pci_reset_bus(to_reset);
+ if (ret)
+ return;

- vfio_device_put(&tmp->vdev);
+ list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
+ cur->needs_reset = false;
+ if (cur->pdev != to_reset && !disable_idle_d3)
+ vfio_pci_set_power_state(cur, PCI_D3hot);
}
-
- kfree(devs.devices);
}

static void __exit vfio_pci_cleanup(void)