Message-ID: <1039604701.20131216162353@eikelenboom.it>
Date:	Mon, 16 Dec 2013 16:23:53 +0100
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	xen-devel@...ts.xenproject.org, <gordan@...ich.net>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [RFC PATCH] Xen PCI back - do slot and bus reset (v0).


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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