Re: [Xen-devel] [PATCH v5 9/9] xen/pciback: Implement PCI reset slot or bus with 'do_flr' SysFS attribute

From: Sander Eikelenboom
Date: Thu Dec 04 2014 - 09:09:17 EST

Thursday, December 4, 2014, 2:43:06 PM, you wrote:

> On 04/12/14 13:10, Sander Eikelenboom wrote:
>> Thursday, December 4, 2014, 1:24:47 PM, you wrote:
>>> On 04/12/14 12:06, Konrad Rzeszutek Wilk wrote:
>>>> On Dec 4, 2014 6:30 AM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
>>>>> On 03/12/14 21:40, Konrad Rzeszutek Wilk wrote:
>>>>>> Instead of doing all this complex dance, we depend on the toolstack
>>>>>> doing the right thing. As such implement the 'do_flr' SysFS attribute
>>>>>> which 'xl' uses when a device is detached or attached from/to a guest.
>>>>>> It bypasses the need to worry about the PCI lock.
>>>>> No. Get pciback to add its own "reset" sysfs file (as I have repeatedly
>>>>> proposed).
>>>> Which does not work as the kobj will complain (as there is already an 'reset' associated with the PCI device).
>>> It is only needed if the core won't provide one.
>>> +static int pcistub_try_create_reset_file(struct pci_dev *pci)
>>> +{
>>> + struct xen_pcibk_dev_data *dev_data = pci_get_drvdata(pci);
>>> + struct device *dev = &pci->dev;
>>> + int ret;
>>> +
>>> + /* Already have a per-function reset? */
>>> + if (pci_probe_reset_function(pci) == 0)
>>> + return 0;
>>> +
>>> + ret = device_create_file(dev, &dev_attr_reset);
>>> + if (ret < 0)
>>> + return ret;
>> + dev_data->>created_reset_file = true;
>>> + return 0;
>>> +}
>> Wouldn't the "core-reset-sysfs-file" be still wired to the end up calling
>> "pci.c:__pci_dev_reset" ?
>> The problem with that function is that from my testing it seems that the
>> first option "pci_dev_specific_reset" always seems to return succes, so all the
>> other options are skipped (flr, pm, slot, bus). However the device it self is
>> not properly reset enough (perhaps the pci_dev_specific_reset is good enough for
>> none virtualization purposes and it's probably the least intrusive. For
>> virtualization however it would be nice to be sure it resets properly, or have a
>> way to force a specific reset routine.)

> Then you need work with the maintainer for those specific devices or
> drivers to fix their specific reset function.

> I'm not adding stuff to pciback to workaround broken quirks.

OK that's a pretty clear message there, so if one wants to use pci and vga
passthrough one should better use KVM and vfio-pci.

vfio-pci has:
- logic to do the try-slot-bus-reset logic
- it has quirks specific to vga passthrough
implemented in from the looks of it a quite clean driver.
(the main issue with it so far was you could only seize devices based on
vendor and device id, which can be a problem when you have multiple devices.
However that was resolved recently if i am correct.)

And neither of those will be supported by xen-pciback if i get your message
right ?


> David

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