From: Dexuan Cui <decui@microsoft.com>
Date: Mon, 27 Mar 2023 21:51:21 -0700
Patch-mainline: not yet, https://lwn.net/ml/linux-kernel/20230328045122.25850-1-decui%40microsoft.com/
Subject: PCI: hv: Add a per-bus mutex state_lock
References: bsc#1207001

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>
Acked-by: Olaf Hering <ohering@suse.de>
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -481,7 +481,10 @@ struct hv_pcibus_device {
 	struct pci_sysdata sysdata;
 	/* 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;
@@ -2289,6 +2292,8 @@ static void pci_devices_present_work(str
 	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) {
@@ -2370,6 +2375,8 @@ static void pci_devices_present_work(str
 		break;
 	}
 
+	mutex_unlock(&hbus->state_lock);
+
 	kfree(dr);
 }
 
@@ -2518,6 +2525,8 @@ static void hv_eject_device_work(struct
 	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
@@ -2554,6 +2563,8 @@ static void hv_eject_device_work(struct
 	put_pcichild(hpdev);
 	put_pcichild(hpdev);
 	/* hpdev has been freed. Do not use it any more. */
+
+	mutex_unlock(&hbus->state_lock);
 }
 
 /**
@@ -3313,6 +3324,7 @@ static int hv_pci_probe(struct hv_device
 	hbus = (struct hv_pcibus_device *)get_zeroed_page(GFP_KERNEL);
 	if (!hbus)
 		return -ENOMEM;
+	mutex_init(&hbus->state_lock);
 	hbus->state = hv_pcibus_init;
 	hbus->wslot_res_allocated = -1;
 
@@ -3410,9 +3422,11 @@ static int hv_pci_probe(struct hv_device
 	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)
@@ -3430,12 +3444,15 @@ static int hv_pci_probe(struct hv_device
 	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: