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: <20180916114306.GF18222@reaktio.net>
Date:   Sun, 16 Sep 2018 14:43:06 +0300
From:   Pasi Kärkkäinen <pasik@....fi>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
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

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?


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


> -boris
>


Thanks,

-- Pasi