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

[Sander Eikelenboom]

Monday, December 16, 2013, 4:36:12 PM, you wrote:

> On Mon, Dec 16, 2013 at 04:23:53PM +0100, Sander Eikelenboom wrote:
>> 
>> 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)

> That is actually what I based it on :-)

Perhaps noteworthy then: [PATCH] pci: Add "try" reset interfaces
http://lkml.indiana.edu/hypermail/linux/kernel/1312.2/00577.html

>> 
>> >> 
>> >> 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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