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: <a726840b-8a5c-0890-73c6-3a95a7205153@oracle.com>
Date:   Mon, 17 Sep 2018 14:06:02 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Pasi Kärkkäinen <pasik@....fi>
Cc:     Jan Beulich <JBeulich@...e.com>,
        Govinda Tatti <Govinda.Tatti@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, bhelgaas@...gle.com,
        xen-devel@...ts.xenproject.org, roger.pau@...rix.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH V3 2/2] Xen/PCIback: Implement PCI
 flr/slot/bus reset with 'reset' SysFS attribute

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.

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.


-boris


>
>
> Meanwhile the pcie_has_flr() has been exported in upstream Linux kernel, so that's already available for use now.
>
> "PCI: Export pcie_has_flr()":
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2d2917f7747805a1f4188672f308d82a8ba01700
>
>
>