linux-kernel - Re: [PATCH v2] PCI: Introduce flag for detached virtual functions

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Date:   Thu, 13 Aug 2020 15:28:51 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        "Oliver O'Halloran" <oohall@...il.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, pmorel@...ux.ibm.com,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-s390@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Alexey Kardashevskiy <aik@...abs.ru>
Subject: Re: [PATCH v2] PCI: Introduce flag for detached virtual functions



On 8/13/20 3:11 PM, Matthew Rosato wrote:
> On 8/13/20 8:34 AM, Niklas Schnelle wrote:
>>
>>
>> On 8/13/20 12:40 PM, Niklas Schnelle wrote:
>>>
>>>
>>> On 8/13/20 11:59 AM, Oliver O'Halloran wrote:
>>>> On Thu, Aug 13, 2020 at 7:00 PM Niklas Schnelle <schnelle@...ux.ibm.com> wrote:
>>>>>
>>>>>
>>>>> On 8/13/20 3:55 AM, Oliver O'Halloran wrote:
>>>>>> On Thu, Aug 13, 2020 at 5:21 AM Matthew Rosato <mjrosato@...ux.ibm.com> wrote:
>>>>>>> *snip*
>>>>>>> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
>>>>>>> index 3902c9f..04ac76d 100644
>>>>>>> --- a/arch/s390/pci/pci.c
>>>>>>> +++ b/arch/s390/pci/pci.c
>>>>>>> @@ -581,6 +581,14 @@ int pcibios_enable_device(struct pci_dev *pdev, int mask)
>>>>>>>   {
>>>>>>>          struct zpci_dev *zdev = to_zpci(pdev);
>>>>>>>
>>>>>>> +       /*
>>>>>>> +        * If we have a VF on a non-multifunction bus, it must be a VF that is
>>>>>>> +        * detached from its parent PF.  We rely on firmware emulation to
>>>>>>> +        * provide underlying PF details.
>>>>>>> +        */
>>>>>>> +       if (zdev->vfn && !zdev->zbus->multifunction)
>>>>>>> +               pdev->detached_vf = 1;
>>>>>>
>>>>>> The enable hook seems like it's a bit too late for this sort of
>>>>>> screwing around with the pci_dev. Anything in the setup path that
>>>>>> looks at ->detached_vf would see it cleared while anything that looks
>>>>>> after the device is enabled will see it set. Can this go into
>>>>>> pcibios_add_device() or a fixup instead?
>>>>>>
>>>>>
>>>>> This particular check could go into pcibios_add_device() yes.
>>>>> We're also currently working on a slight rework of how
>>>>> we establish the VF to parent PF linking including the sysfs
>>>>> part of that. The latter sadly can only go after the sysfs
>>>>> for the virtfn has been created and that only happens
>>>>> after all fixups. We would like to do both together because
>>>>> the latter sets pdev->is_virtfn which I think is closely related.
>>>>>
>>>>> I was thinking of starting another discussion
>>>>> about adding a hook that is executed just after the sysfs entries
>>>>> for the PCI device are created but haven't yet.
>>>>
>>>> if all you need is sysfs then pcibios_bus_add_device() or a bus
>>>> notifier should work
>>>
>>> So this might go a bit off track but the problem is that
>>> on s390 a VF can be disabled and reenabled with disable_slot()/enable_slot().
>>> In this case pcibios_bus_add_device() is not called again but
>>> the PF/VF link needs to be reestablished.
>>
>> Scratch that I must have made some stupid mistake last time I tried
>> this, with your suggestion I tried again and it works perfectly
>> moving the setup into pcibios_bus_add_device().
>> Thank you, this is actually much nicer!
>>
> 
> OK, and I can likewise relocate the setting of detached_vf to pcibios_bus_add_device().
> 
Yes and I would suggest we add it in arch/s390/pci_bus.c just
after the the setup_virtfn stuff, then that can stay static
and the fix minimal.
I'll send a new version of my patches internally later, still
running it on the different configurations.