Re: [Xen-devel] [RFC PATCH] Xen PCI back - do slot and bus reset (v0).

[David Vrabel <david.vrabel@citrix.com>]

On 13/12/13 16:09, Konrad Rzeszutek Wilk wrote:
> Hey,
> 
> While I was trying to narrow down the state of GPU passthrough
> (still not finished) and figuring what needs to be done I realized
> that Xen PCIback did not reset my GPU properly (when I crashed the
> Windows guest by mistake). It does an FLR reset or Power one - if
> the device supports it. But it seems that some of these GPUs
> are liars and actually don't do the power part properly.

In my experience the devices do not lie.  They correctly report that
they do not perform a reset in D3hot.

Here's the patch I'm using to solve this.  It does something similar.
i.e., a SBR if all devices on that bus are safe to be reset.

I prefer it because it provides the standard 'reset' sysfs file that the
toolstack/userspace can use.

It does have some limitations:  a) It does not check whether a device is
in use (only if it is bound to pciback); and b) it hand rolls
pci_slot_reset() (because it didn't exist at the time).

diff --git a/drivers/xen/xen-pciback/pci_stub.c
b/drivers/xen/xen-pciback/pci_stub.c
index 4e8ba38..5a03e63 100644
--- a/drivers/xen/xen-pciback/pci_stub.c
+++ b/drivers/xen/xen-pciback/pci_stub.c
@@ -14,6 +14,7 @@
 #include <linux/wait.h>
 #include <linux/sched.h>
 #include <linux/atomic.h>
+#include <linux/delay.h>
 #include <xen/events.h>
 #include <asm/xen/pci.h>
 #include <asm/xen/hypervisor.h>
@@ -43,6 +44,7 @@ struct pcistub_device {
 	struct kref kref;
 	struct list_head dev_list;
 	spinlock_t lock;
+	bool created_reset_file;

 	struct pci_dev *dev;
 	struct xen_pcibk_device *pdev;/* non-NULL if struct pci_dev is in use */
@@ -60,6 +62,114 @@ static LIST_HEAD(pcistub_devices);
 static int initialize_devices;
 static LIST_HEAD(seized_devices);

+/*
+ * pci_reset_function() will only work if there is a mechanism to
+ * reset that single function (e.g., FLR or a D-state transition).
+ * For PCI hardware that has two or more functions but no per-function
+ * reset, we can do a bus reset iff all the functions are co-assigned
+ * to the same domain.
+ *
+ * If a function has no per-function reset mechanism the 'reset' sysfs
+ * file that the toolstack uses to reset a function prior to assigning
+ * the device will be missing.  In this case, pciback adds its own
+ * which will try a bus reset.
+ *
+ * Note: pciback does not check for co-assigment before doing a bus
+ * reset, only that the devices are bound to pciback.  The toolstack
+ * is assumed to have done the right thing.
+ */
+static int __pcistub_reset_function(struct pci_dev *dev)
+{
+	struct pci_dev *pdev;
+	u16 ctrl;
+	int ret;
+
+	ret = __pci_reset_function_locked(dev);
+	if (ret == 0)
+		return 0;
+
+	if (pci_is_root_bus(dev->bus) || dev->subordinate || !dev->bus->self)
+		return -ENOTTY;
+
+	list_for_each_entry(pdev, &dev->bus->devices, bus_list) {
+		if (pdev != dev && (!pdev->driver
+				    || strcmp(pdev->driver->name, "pciback")))
+			return -ENOTTY;
+		pci_save_state(pdev);
+	}
+
+	pci_read_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, &ctrl);
+	ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
+	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
+	msleep(200);
+
+	ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
+	pci_write_config_word(dev->bus->self, PCI_BRIDGE_CONTROL, ctrl);
+	msleep(200);
+
+	list_for_each_entry(pdev, &dev->bus->devices, bus_list)
+		pci_restore_state(pdev);
+
+	return 0;
+}
+
+static int pcistub_reset_function(struct pci_dev *dev)
+{
+	int ret;
+
+	device_lock(&dev->dev);
+	ret = __pcistub_reset_function(dev);
+	device_unlock(&dev->dev);
+
+	return ret;
+}
+
+static ssize_t pcistub_reset_store(struct device *dev,
+				   struct device_attribute *attr,
+				   const char *buf, size_t count)
+{
+	struct pci_dev *pdev = to_pci_dev(dev);
+	unsigned long val;
+	ssize_t result = strict_strtoul(buf, 0, &val);
+
+	if (result < 0)
+		return result;
+
+	if (val != 1)
+		return -EINVAL;
+
+	result = pcistub_reset_function(pdev);
+	if (result < 0)
+		return result;
+	return count;
+}
+static DEVICE_ATTR(reset, 0200, NULL, pcistub_reset_store);
+
+static int pcistub_try_create_reset_file(struct pcistub_device *psdev)
+{
+	struct device *dev = &psdev->dev->dev;
+	struct sysfs_dirent *reset_dirent;
+	int ret;
+
+	reset_dirent = sysfs_get_dirent(dev->kobj.sd, NULL, "reset");
+	if (reset_dirent) {
+		sysfs_put(reset_dirent);
+		return 0;
+	}
+
+	ret = device_create_file(dev, &dev_attr_reset);
+	if (ret < 0)
+		return ret;
+	psdev->created_reset_file = true;
+	return 0;
+}
+
+static void pcistub_remove_reset_file(struct pcistub_device *psdev)
+{
+	if (psdev && psdev->created_reset_file)
+		device_remove_file(&psdev->dev->dev, &dev_attr_reset);
+}
+
 static struct pcistub_device *pcistub_device_alloc(struct pci_dev *dev)
 {
 	struct pcistub_device *psdev;
@@ -95,12 +205,15 @@ static void pcistub_device_release(struct kref *kref)

 	dev_dbg(&dev->dev, "pcistub_device_release\n");

+	pcistub_remove_reset_file(psdev);
+
 	xen_unregister_device_domain_owner(dev);

 	/* Call the reset function which does not take lock as this
 	 * is called from "unbind" which takes a device_lock mutex.
 	 */
-	__pci_reset_function_locked(dev);
+	__pcistub_reset_function(psdev->dev);
+
 	if (pci_load_and_free_saved_state(dev, &dev_data->pci_saved_state))
 		dev_dbg(&dev->dev, "Could not reload PCI state\n");
 	else
@@ -268,7 +381,7 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
 	/* This is OK - we are running from workqueue context
 	 * and want to inhibit the user from fiddling with 'reset'
 	 */
-	pci_reset_function(dev);
+	pcistub_reset_function(psdev->dev);
 	pci_restore_state(psdev->dev);

 	/* This disables the device. */
@@ -392,7 +505,7 @@ static int pcistub_init_device(struct pci_dev *dev)
 		dev_err(&dev->dev, "Could not store PCI conf saved state!\n");
 	else {
 		dev_dbg(&dev->dev, "resetting (FLR, D3, etc) the device\n");
-		__pci_reset_function_locked(dev);
+		__pcistub_reset_function(dev);
 		pci_restore_state(dev);
 	}
 	/* Now disable the device (this also ensures some private device
@@ -467,6 +580,10 @@ static int pcistub_seize(struct pci_dev *dev)
 	if (!psdev)
 		return -ENOMEM;

+	err = pcistub_try_create_reset_file(psdev);
+	if (err < 0)
+		goto out;
+
 	spin_lock_irqsave(&pcistub_devices_lock, flags);

 	if (initialize_devices) {
@@ -485,10 +602,9 @@ static int pcistub_seize(struct pci_dev *dev)
 	}

 	spin_unlock_irqrestore(&pcistub_devices_lock, flags);
-
+out:
 	if (err)
 		pcistub_device_put(psdev);
-
 	return err;
 }