PCI: hv: Fix a timing issue which causes kdump to fail occasionally

Kdump could fail sometime on Hyper-V guest because the retry in
hv_pci_enter_d0() releases child device structures in hv_pci_bus_exit().

Although there is a second asynchronous device relations message sending
from the host, if this message arrives to the guest after
hv_send_resource_allocated() is called, the retry would fail.

Fix the problem by moving retry to hv_pci_probe() and start the retry
from hv_pci_query_relations() call.  This will cause a device relations
message to arrive to the guest synchronously; the guest would then be
able to rebuild the child device structures before calling
hv_send_resource_allocated().

Link: https://lore.kernel.org/r/20200727071731.18516-1-weh@microsoft.com
Fixes: c81992e7 ("PCI: hv: Retry PCI bus D0 entry on invalid device state")
Signed-off-by: Wei Hu <weh@microsoft.com>
[lorenzo.pieralisi@arm.com: fixed a comment and commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>

drivers/pci/controller/pci-hyperv.c

@@ -2759,10 +2759,8 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	struct pci_bus_d0_entry *d0_entry;
 	struct hv_pci_compl comp_pkt;
 	struct pci_packet *pkt;
-	bool retry = true;
 	int ret;
 
-enter_d0_retry:
 	/*
 	 * Tell the host that the bus is ready to use, and moved into the
 	 * powered-on state.  This includes telling the host which region
@@ -2789,38 +2787,6 @@ static int hv_pci_enter_d0(struct hv_device *hdev)
 	if (ret)
 		goto exit;
 
-	/*
-	 * In certain case (Kdump) the pci device of interest was
-	 * not cleanly shut down and resource is still held on host
-	 * side, the host could return invalid device status.
-	 * We need to explicitly request host to release the resource
-	 * and try to enter D0 again.
-	 */
-	if (comp_pkt.completion_status < 0 && retry) {
-		retry = false;
-
-		dev_err(&hdev->device, "Retrying D0 Entry\n");
-
-		/*
-		 * Hv_pci_bus_exit() calls hv_send_resource_released()
-		 * to free up resources of its child devices.
-		 * In the kdump kernel we need to set the
-		 * wslot_res_allocated to 255 so it scans all child
-		 * devices to release resources allocated in the
-		 * normal kernel before panic happened.
-		 */
-		hbus->wslot_res_allocated = 255;
-
-		ret = hv_pci_bus_exit(hdev, true);
-
-		if (ret == 0) {
-			kfree(pkt);
-			goto enter_d0_retry;
-		}
-		dev_err(&hdev->device,
-			"Retrying D0 failed with ret %d\n", ret);
-	}
-
 	if (comp_pkt.completion_status < 0) {
 		dev_err(&hdev->device,
 			"PCI Pass-through VSP failed D0 Entry with status %x\n",
@@ -3058,6 +3024,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 	struct hv_pcibus_device *hbus;
 	u16 dom_req, dom;
 	char *name;
+	bool enter_d0_retry = true;
 	int ret;
 
 	/*
@@ -3178,11 +3145,47 @@ static int hv_pci_probe(struct hv_device *hdev,
 	if (ret)
 		goto free_fwnode;
 
+retry:
 	ret = hv_pci_query_relations(hdev);
 	if (ret)
 		goto free_irq_domain;
 
 	ret = hv_pci_enter_d0(hdev);
+	/*
+	 * In certain case (Kdump) the pci device of interest was
+	 * not cleanly shut down and resource is still held on host
+	 * side, the host could return invalid device status.
+	 * We need to explicitly request host to release the resource
+	 * and try to enter D0 again.
+	 * Since the hv_pci_bus_exit() call releases structures
+	 * of all its child devices, we need to start the retry from
+	 * hv_pci_query_relations() call, requesting host to send
+	 * the synchronous child device relations message before this
+	 * information is needed in hv_send_resources_allocated()
+	 * call later.
+	 */
+	if (ret == -EPROTO && enter_d0_retry) {
+		enter_d0_retry = false;
+
+		dev_err(&hdev->device, "Retrying D0 Entry\n");
+
+		/*
+		 * Hv_pci_bus_exit() calls hv_send_resources_released()
+		 * to free up resources of its child devices.
+		 * In the kdump kernel we need to set the
+		 * wslot_res_allocated to 255 so it scans all child
+		 * devices to release resources allocated in the
+		 * normal kernel before panic happened.
+		 */
+		hbus->wslot_res_allocated = 255;
+		ret = hv_pci_bus_exit(hdev, true);
+
+		if (ret == 0)
+			goto retry;
+
+		dev_err(&hdev->device,
+			"Retrying D0 failed with ret %d\n", ret);
+	}
 	if (ret)
 		goto free_irq_domain;