RE: [PATCH v2 5/6] PCI: hv: Add a per-bus mutex state_lock

From: Dexuan Cui decui@microsoft.com Sent: Monday, April 3, 2023 7:06 PM

In the case of fast device addition/removal, it's possible that hv_eject_device_work() can start to run before create_root_hv_pci_bus() starts to run; as a result, the pci_get_domain_bus_and_slot() in hv_eject_device_work() can return a 'pdev' of NULL, and hv_eject_device_work() can remove the 'hpdev', and immediately send a message PCI_EJECTION_COMPLETE to the host, and the host immediately unassigns the PCI device from the guest; meanwhile, create_root_hv_pci_bus() and the PCI device driver can be probing the dead PCI device and reporting timeout errors.

Fix the issue by adding a per-bus mutex 'state_lock' and grabbing the mutex before powering on the PCI bus in hv_pci_enter_d0(): when hv_eject_device_work() starts to run, it's able to find the 'pdev' and call pci_stop_and_remove_bus_device(pdev): if the PCI device driver has loaded, the PCI device driver's probe() function is already called in create_root_hv_pci_bus() -> pci_bus_add_devices(), and now hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to call the PCI device driver's remove() function and remove the device reliably; if the PCI device driver hasn't loaded yet, the function call hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to remove the PCI device reliably and the PCI device driver's probe() function won't be called; if the PCI device driver's probe() is already running (e.g., systemd-udev is loading the PCI device driver), it must be holding the per-device lock, and after the probe() finishes and releases the lock, hv_eject_device_work() -> pci_stop_and_remove_bus_device() is able to proceed to remove the device reliably.

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs") Signed-off-by: Dexuan Cui decui@microsoft.com Cc: stable@vger.kernel.org

---

v2: Removed the "debug code". Fixed the "goto out" in hv_pci_resume() [Michael Kelley] Added Cc:stable

drivers/pci/controller/pci-hyperv.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 48feab095a144..3ae2f99dea8c2 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -489,7 +489,10 @@ struct hv_pcibus_device { struct fwnode_handle *fwnode; /* Protocol version negotiated with the host */ enum pci_protocol_version_t protocol_version;

• struct mutex state_lock; enum hv_pcibus_state state;
• struct hv_device *hdev; resource_size_t low_mmio_space; resource_size_t high_mmio_space;

@@ -2512,6 +2515,8 @@ static void pci_devices_present_work(struct work_struct *work) if (!dr) return;

• mutex_lock(&hbus->state_lock);
• /* First, mark all existing children as reported missing. */ spin_lock_irqsave(&hbus->device_list_lock, flags); list_for_each_entry(hpdev, &hbus->children, list_entry) {

@@ -2593,6 +2598,8 @@ static void pci_devices_present_work(struct work_struct *work) break; }

• mutex_unlock(&hbus->state_lock);
• kfree(dr);

}

@@ -2741,6 +2748,8 @@ static void hv_eject_device_work(struct work_struct *work) hpdev = container_of(work, struct hv_pci_dev, wrk); hbus = hpdev->hbus;

• mutex_lock(&hbus->state_lock);
• /*
  • Ejection can come before or after the PCI bus has been set up, so
  • attempt to find it and tear down the bus state, if it exists. This

@@ -2777,6 +2786,8 @@ static void hv_eject_device_work(struct work_struct *work) put_pcichild(hpdev); put_pcichild(hpdev); /* hpdev has been freed. Do not use it any more. */

• mutex_unlock(&hbus->state_lock);

}

/** @@ -3562,6 +3573,7 @@ static int hv_pci_probe(struct hv_device *hdev, return -ENOMEM;

hbus->bridge = bridge;

• mutex_init(&hbus->state_lock); hbus->state = hv_pcibus_init; hbus->wslot_res_allocated = -1;

@@ -3670,9 +3682,11 @@ static int hv_pci_probe(struct hv_device *hdev, if (ret) goto free_irq_domain;

• mutex_lock(&hbus->state_lock);
• ret = hv_pci_enter_d0(hdev); if (ret)

• goto free_irq_domain;
  

• goto release_state_lock;
  
  

  ret = hv_pci_allocate_bridge_windows(hbus); if (ret)

@@ -3690,12 +3704,15 @@ static int hv_pci_probe(struct hv_device *hdev, if (ret) goto free_windows;

• mutex_unlock(&hbus->state_lock); return 0;

free_windows: hv_pci_free_bridge_windows(hbus); exit_d0: (void) hv_pci_bus_exit(hdev, true); +release_state_lock:

• mutex_unlock(&hbus->state_lock);

free_irq_domain: irq_domain_remove(hbus->irq_domain); free_fwnode: @@ -3945,20 +3962,26 @@ static int hv_pci_resume(struct hv_device *hdev) if (ret) goto out;

• mutex_lock(&hbus->state_lock);
• ret = hv_pci_enter_d0(hdev); if (ret)

• goto out;
  

• goto release_state_lock;
  
  

  ret = hv_send_resources_allocated(hdev); if (ret)

• goto out;
  

• goto release_state_lock;
  
  

  prepopulate_bars(hbus);

  hv_pci_restore_msi_state(hbus);

  hbus->state = hv_pcibus_installed;

• mutex_unlock(&hbus->state_lock); return 0;

+release_state_lock:

• mutex_unlock(&hbus->state_lock);

out: vmbus_close(hdev->channel); return ret; -- 2.25.1

Reviewed-by: Michael Kelley mikelley@microsoft.com