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

[Konrad Rzeszutek Wilk]

On Mon, Dec 16, 2013 at 10:59:01AM +0000, David Vrabel wrote:
> 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.

We can still add the 'reset' to SysFS
> 
> 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).

.. which can have those limiations removed and be based on this patchset.
Meaning it won't do a bus-reset or device reset if the rest of the devices
are _not_ assigned to pciback.

> 
> 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;
>  }
> 
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