linux-kernel - Re: [Xen-devel] [PATCH V3 2/2] Xen/PCIback: Implement PCI flr/slot/bus reset with 'reset' SysFS attribute

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Message-ID: <5E7DDB68-4E68-48A5-AEEC-EE1B21A50E9E@citrix.com>
Date:   Tue, 18 Sep 2018 09:32:09 +0000
From:   George Dunlap <George.Dunlap@...rix.com>
To:     Pasi Kärkkäinen <pasik@....fi>
CC:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jan Beulich <JBeulich@...e.com>,
        Juergen Gross <jgross@...e.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Roger Pau Monne <roger.pau@...rix.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        George Dunlap <George.Dunlap@...rix.com>
Subject: Re: [Xen-devel] [PATCH V3 2/2] Xen/PCIback: Implement PCI
 flr/slot/bus reset with 'reset' SysFS attribute



> On Sep 18, 2018, at 8:15 AM, Pasi Kärkkäinen <pasik@....fi> wrote:
> 
> Hi,
> 
> On Mon, Sep 17, 2018 at 02:06:02PM -0400, Boris Ostrovsky wrote:
>> On 9/16/18 7:43 AM, Pasi Kärkkäinen wrote:
>>> Hi,
>>> 
>>> On Mon, Dec 18, 2017 at 12:32:11PM -0500, Boris Ostrovsky wrote:
>>>> On 12/18/2017 02:36 AM, Jan Beulich wrote:
>>>>>>>> On 15.12.17 at 20:52, <Govinda.Tatti@...cle.COM> wrote:
>>>>>>>>> +static int pcistub_device_reset(struct pci_dev *dev)
>>>>>>>>> +{
>>>>>>>>> +	struct xen_pcibk_dev_data *dev_data;
>>>>>>>>> +	bool slot = false, bus = false;
>>>>>>>>> +	struct pcistub_args arg = {};
>>>>>>>>> +
>>>>>>>>> +	if (!dev)
>>>>>>>>> +		return -EINVAL;
>>>>>>>>> +
>>>>>>>>> +	dev_dbg(&dev->dev, "[%s]\n", __func__);
>>>>>>>>> +
>>>>>>>>> +	/* First check and try FLR */
>>>>>>>>> +	if (pcie_has_flr(dev)) {
>>>>>>>>> +		dev_dbg(&dev->dev, "resetting %s device using FLR\n",
>>>>>>>>> +			pci_name(dev));
>>>>>>>>> +		pcie_flr(dev);
>>>>>>>> The lack of error check here puzzled me, but I see the function
>>>>>>>> indeed returns void right now. I think the prereq patch should
>>>>>>>> change this along with exporting the function - you really don't
>>>>>>>> want the device to be handed to a guest when the FLR timed
>>>>>>>> out.
>>>>>>> We will change pcie_flr() to return error code. I will make this change
>>>>>>> in the next version of this patch.
>>>>>> I exchanged some emails with Bjorn/Christoph and it looks like Christoph
>>>>>> as some planto restructure pcie flr specific functions but I don't know
>>>>>> the exact time-frame. For now,I am planning to use existing pcie_flr()
>>>>>> after checking FLR capability. We will switchto revised pcie_flr() once
>>>>>> it is available.
>>>>>> 
>>>>>> I hope you are fine with this approach. Please let me know. Thanks.
>>>>> I've seen that other discussion. I don't think the change here
>>>>> should be done prior to the error reporting being put in place,
>>>>> for security reasons. But in the end it'll be Konrad as the
>>>>> maintainer to judge.
>>>>> 
>>>>> Or wait, looks like there's some confusion in ./MAINTAINERS:
>>>>> Konrad is listed as maintainer for "XEN PCI SUBSYSTEM", but the
>>>>> list of files doesn't include pciback. So it would instead be Boris
>>>>> or Jürgen to give you a final word.
>>>> 
>>>> This is now 4.16 material so we can at least wait until closer to
>>>> opening of the merge window when we may have the PCI updates. (And I
>>>> just noticed that you responded to Christoph.)
>>>> 
>>>> Besides, we don't want to make kernel changes until the interface is
>>>> settled (i.e the toolstack changes are accepted).
>>>> 
>>> It seems Govinda's email address is giving an error, so I assume someone else needs to pick up this pciback 'reset' feature.
>>> Is it likely someone else from Oracle can/will pick up and refresh this patch, with the review comments addressed?
>> 
>> 
>> Govinda is no longer at Oracle.
>> 
> 
> Yep, thought so. Removed from CC list.
> 
> 
>> What about the toolstack changes? Have they been accepted? I vaguely
>> recall there was a discussion about those changes but don't remember how
>> it ended.
>> 
> 
> I don't think toolstack/libxl patch has been applied yet either.
> 
> 
> "[PATCH V1 0/1] Xen/Tools: PCI reset using 'reset' SysFS attribute":
> https://lists.xen.org/archives/html/xen-devel/2017-12/msg00664.html
> 
> "[PATCH V1 1/1] Xen/libxl: Perform PCI reset using 'reset' SysFS attribute":
> https://lists.xen.org/archives/html/xen-devel/2017-12/msg00663.html
> 
> George asked for some clarifications:
> https://lists.xen.org/archives/html/xen-devel/2017-12/msg01044.html
> https://lists.xen.org/archives/html/xen-devel/2017-12/msg01116.html

Right, the description of the patch didn’t actually tell you what was going on.  It should have said something like, “xl currently attempts to reset a device using X; but that’s never been implemented in Linux.  Instead, use Y, which [is better for whatever reason]”.

 -George