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

From: Sander Eikelenboom
Date: Mon Dec 16 2013 - 10:24:02 EST


Monday, December 16, 2013, 3:35:15 PM, you wrote:

> 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.

Perhaps there is something to learn from the steps vfio-pci takes to do this ?
(they sorted out quite some stuff around pci/vga passtrough)

>>
>> 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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