Date:   Wed, 19 Jan 2022 18:22:07 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     Lukasz Maniak <lukasz.maniak@...ux.intel.com>,
        Bjorn Helgaas <helgaas@...nel.org>
CC:     <yangyicong@...ilicon.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Łukasz Gieryk <lukasz.gieryk@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH] PCI: Reset IOV state on FLR to PF

Hi Lukasz, Bjorn,

FYI, I tested with Mellanox CX-5, the VF also exists after FLR. Here's the operation:

[root@...alhost ~]# lspci  -s 01:
01:00.0 Ethernet controller: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
01:00.1 Ethernet controller: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
[root@...alhost ~]# lspci -vvv -s 01:00.0 | egrep "IOV|VF"
        Capabilities: [180 v1] Single Root I/O Virtualization (SR-IOV)
                IOVCap: Migration- 10BitTagReq- Interrupt Message Number: 000
                IOVCtl: Enable- Migration- Interrupt- MSE- ARIHierarchy+ 10BitTagReq-
                IOVSta: Migration-
                Initial VFs: 16, Total VFs: 16, Number of VFs: 0, Function Dependency Link: 00
                VF offset: 2, stride: 1, Device ID: 101a
                VF Migration: offset: 00000000, BIR: 0
[root@...alhost 0000:01:00.0]# echo 1 > sriov_numvfs
[root@...alhost ~]# lspci -vvv -s 01:00.0 | egrep "IOV|VF"
        Capabilities: [180 v1] Single Root I/O Virtualization (SR-IOV)
                IOVCap: Migration- 10BitTagReq- Interrupt Message Number: 000
                IOVCtl: Enable+ Migration- Interrupt- MSE+ ARIHierarchy+ 10BitTagReq-
                IOVSta: Migration-
                Initial VFs: 16, Total VFs: 16, Number of VFs: 1, Function Dependency Link: 00
                VF offset: 2, stride: 1, Device ID: 101a
                VF Migration: offset: 00000000, BIR: 0
[root@...alhost 0000:01:00.0]# echo 1 > reset
[root@...alhost ~]# lspci -vvv -s 01:00.0 | egrep "IOV|VF"
        Capabilities: [180 v1] Single Root I/O Virtualization (SR-IOV)
                IOVCap: Migration- 10BitTagReq- Interrupt Message Number: 000
                IOVCtl: Enable+ Migration- Interrupt- MSE+ ARIHierarchy+ 10BitTagReq-
                IOVSta: Migration-
                Initial VFs: 16, Total VFs: 16, Number of VFs: 1, Function Dependency Link: 00
                VF offset: 2, stride: 1, Device ID: 101a
                VF Migration: offset: 00000000, BIR: 0
[root@...alhost ~]# lspci -xxx -s 01:00.0
01:00.0 Ethernet controller: Mellanox Technologies MT28800 Family [ConnectX-5 Ex]
00: b3 15 19 10 46 05 10 00 00 00 00 02 08 00 80 00
10: 0c 00 00 00 00 08 00 00 00 00 00 00 00 00 00 00
20: 00 00 00 00 00 00 00 00 00 00 00 00 b3 15 08 00
30: 00 00 70 e6 60 00 00 00 00 00 00 00 ff 01 00 00
40: 01 00 c3 81 08 00 00 00 03 9c cc 80 00 78 00 00
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 20 00 01
60: 10 48 02 00 e2 8f e0 11 5f 29 00 00 04 71 41 00
70: 08 00 04 11 00 00 00 00 00 00 00 00 00 00 00 00
80: 00 00 00 00 17 00 01 00 40 00 00 00 1e 00 80 01
90: 04 00 1e 00 00 00 00 00 00 00 00 00 11 c0 3f 80
a0: 00 20 00 00 00 30 00 00 00 00 00 00 00 00 00 00
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
c0: 09 40 18 00 0a 00 00 20 f0 1a 00 00 00 00 00 00
d0: 20 00 00 80 00 00 00 00 00 00 00 00 00 00 00 00
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[root@...alhost 0000:01:00.0]# cat reset_method
flr bus

On 2022/1/19 10:47, Yicong Yang wrote:
> On 2022/1/19 0:30, Lukasz Maniak wrote:
>> On Tue, Jan 18, 2022 at 07:07:23PM +0800, Yicong Yang wrote:
>>> On 2022/1/18 6:55, Bjorn Helgaas wrote:
>>>> [+cc Alex in case he has comments on how FLR should work on
>>>> non-conforming hns3 devices]
>>>>
>>>> On Sat, Jan 15, 2022 at 05:22:19PM +0800, Yicong Yang wrote:
>>>>> On 2022/1/15 0:37, Bjorn Helgaas wrote:
>>>>>> On Fri, Jan 14, 2022 at 05:42:48PM +0800, Yicong Yang wrote:
>>>>>>> On 2022/1/14 0:45, Lukasz Maniak wrote:
>>>>>>>> On Wed, Jan 12, 2022 at 08:49:03AM -0600, Bjorn Helgaas wrote:
>>>>>>>>> On Wed, Dec 22, 2021 at 08:19:57PM +0100, Lukasz Maniak wrote:
>>>>>>>>>> As per PCI Express specification, FLR to a PF resets the PF state as
>>>>>>>>>> well as the SR-IOV extended capability including VF Enable which means
>>>>>>>>>> that VFs no longer exist.
>>>>>>>>>
>>>>>>>>> Can you add a specific reference to the spec, please?
>>>>>>>>>
>>>>>>>> Following the Single Root I/O Virtualization and Sharing Specification:
>>>>>>>> 2.2.3. FLR That Targets a PF
>>>>>>>> PFs must support FLR.
>>>>>>>> FLR to a PF resets the PF state as well as the SR-IOV extended
>>>>>>>> capability including VF Enable which means that VFs no longer exist.
>>>>>>>>
>>>>>>>> For PCI Express Base Specification Revision 5.0 and later, this is
>>>>>>>> section 9.2.2.3.
>>>>>>
>>>>>> This is also the section in the new PCIe r6.0.  Let's use that.
>>>>>>
>>>>>>>>>> Currently, the IOV state is not updated during FLR, resulting in
>>>>>>>>>> non-compliant PCI driver behavior.
>>>>>>>>>
>>>>>>>>> And include a little detail about what problem is observed?  How would
>>>>>>>>> a user know this problem is occurring?
>>>>>>>>>
>>>>>>>> The problem is that the state of the kernel and HW as to the number of
>>>>>>>> VFs gets out of sync after FLR.
>>>>>>>>
>>>>>>>> This results in further listing, after the FLR is performed by the HW,
>>>>>>>> of VFs that actually no longer exist and should no longer be reported on
>>>>>>>> the PCI bus. lspci return FFs for these VFs.
>>>>>>>
>>>>>>> There're some exceptions. Take HiSilicon's hns3 and sec device as an
>>>>>>> example, the VF won't be destroyed after the FLR reset.
>>>>>>
>>>>>> If FLR on an hns3 PF does *not* clear VF Enable, and the VFs still
>>>>>> exist after FLR, isn't that a violation of sec 9.2.2.3?
>>>>>
>>>>> yes I think it's a violation to the spec.
>>>>
>>>> Thanks for confirming that.
>>>>
>>>>>> If hns3 and sec don't conform to the spec, we should have some sort of
>>>>>> quirk that serves to document and work around this.
>>>>>
>>>>> ok I think it'll help. Do you mean something like this based on this patch:
>>>>>
>>>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>>> index 69ee321027b4..0e4976c669b2 100644
>>>>> --- a/drivers/pci/iov.c
>>>>> +++ b/drivers/pci/iov.c
>>>>> @@ -1025,6 +1025,8 @@ void pci_reset_iov_state(struct pci_dev *dev)
>>>>>  		return;
>>>>>  	if (!iov->num_VFs)
>>>>>  		return;
>>>>> +	if (dev->flr_no_vf_reset)
>>>>> +		return;
>>>>>
>>>>>  	sriov_del_vfs(dev);
>>>>>
>>>>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>>>>> index 003950c738d2..c8ffcb0ac612 100644
>>>>> --- a/drivers/pci/quirks.c
>>>>> +++ b/drivers/pci/quirks.c
>>>>> @@ -1860,6 +1860,17 @@ DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_HUAWEI, 0xa256, quirk_huawei_pcie_sva);
>>>>>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_HUAWEI, 0xa258, quirk_huawei_pcie_sva);
>>>>>  DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_HUAWEI, 0xa259, quirk_huawei_pcie_sva);
>>>>>
>>>>> +/*
>>>>> + * Some HiSilicon PCIe devices' VF won't be destroyed after a FLR reset.
>>>>> + * Don't reset these devices' IOV state when doing FLR.
>>>>> + */
>>>>> +static void quirk_huawei_pcie_flr(struct pci_dev *pdev)
>>>>> +{
>>>>> +	pdev->flr_no_vf_reset = 1;
>>>>> +}
>>>>> +DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_HUAWEI, 0xa255, quirk_huawei_pcie_flr);
>>>>> +/* ...some other devices have this quirk */
>>>>
>>>> Yes, I think something along this line will help.
>>>>
>>>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>>>> index 18a75c8e615c..e62f9fa4d48f 100644
>>>>> --- a/include/linux/pci.h
>>>>> +++ b/include/linux/pci.h
>>>>> @@ -454,6 +454,7 @@ struct pci_dev {
>>>>>  	unsigned int	is_probed:1;		/* Device probing in progress */
>>>>>  	unsigned int	link_active_reporting:1;/* Device capable of reporting link active */
>>>>>  	unsigned int	no_vf_scan:1;		/* Don't scan for VFs after IOV enablement */
>>>>> +	unsigned int	flr_no_vf_reset:1;	/* VF won't be destroyed after PF's FLR */
>>>>>
>>>>>>> Currently the transactions with the VF will be restored after the
>>>>>>> FLR. But this patch will break that, the VF is fully disabled and
>>>>>>> the transaction cannot be restored. User needs to reconfigure it,
>>>>>>> which is unnecessary before this patch.
>>>>>>
>>>>>> What does it mean for a "transaction to be restored"?  Maybe you mean
>>>>>> this patch removes the *VFs* via sriov_del_vfs(), and whoever
>>>>>> initiated the FLR would need to re-enable VFs via pci_enable_sriov()
>>>>>> or something similar?
>>>>>
>>>>> Partly. It'll also terminate the VF users.
>>>>> Think that I attach the VF of hns to a VM by vfio and ping the network
>>>>> in the VM, when doing FLR the 'ping' will pause and after FLR it'll
>>>>> resume. Currenlty The driver handle this in the ->reset_{prepare, done}()
>>>>> methods. The user of VM may not realize there is a FLR of the PF as the
>>>>> VF always exists and the 'ping' is never terminated.
>>>>>
>>>>> If we remove the VF when doing FLR, then 1) we'll block in the VF->remove()
>>>>> until no one is using the device, for example the 'ping' is finished.
>>>>> 2) the VF in the VM no longer exists and we have to re-enable VF and hotplug
>>>>> it into the VM and restart the ping. That's a big difference.
>>>>>
>>>>>> If FLR disables VFs, it seems like we should expect to have to
>>>>>> re-enable them if we want them.
>>>>>
>>>>> It involves a remove()/probe() process of the VF driver and the user
>>>>> of the VF will be terminated, just like the situation illustrated
>>>>> above.
>>>>
>>>> I think users of FLR should be able to rely on it working per spec,
>>>> i.e., that VFs will be destroyed.  If hardware like hns3 doesn't do
>>>> that, the quirk should work around that in software by doing it
>>>> explicitly.
>>>>
>>>> I don't think the non-standard behavior should be exposed to the
>>>> users.  The user should not have to know about this hns3 issue.
>>>>
>>>> If FLR on a standard NIC terminates a ping on a VF, FLR on an hns3 NIC
>>>> should also terminate a ping on a VF.
>>>>
>>>
>>> ok thanks for the discussion, agree on that. According to the spec, after
>>> the FLR to the PF the VF does not exist anymore, so the ping will be terminated.
>>> Our hns3 and sec team are still evaluating it before coming to a solution of
>>> whether using a quirk or comform to the spec.
>>>
>>> For this patch it looks reasonable to me, but some questions about the code below.
>>>
>>>>>>> Can we handle this problem in another way? Maybe test the VF's
>>>>>>> vendor device ID after the FLR reset to see whether it has really
>>>>>>> gone or not?
>>>>>>>
>>>>>>>> sriov_numvfs in sysfs returns old invalid value and does not allow
>>>>>>>> setting a new value before explicitly setting 0 in the first place.
>>>>>>>>
>>>>>>>>>> This patch introduces a simple function, called on the FLR path, that
>>>>>>>>>> removes the virtual function devices from the PCI bus and their
>>>>>>>>>> corresponding sysfs links with a final clear of the num_vfs value in IOV
>>>>>>>>>> state.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Lukasz Maniak <lukasz.maniak@...ux.intel.com>
>>>>>>>>>> ---
>>>>>>>>>>  drivers/pci/iov.c | 21 +++++++++++++++++++++
>>>>>>>>>>  drivers/pci/pci.c |  2 ++
>>>>>>>>>>  drivers/pci/pci.h |  4 ++++
>>>>>>>>>>  3 files changed, 27 insertions(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>>>>>>>> index 0267977c9f17..69ee321027b4 100644
>>>>>>>>>> --- a/drivers/pci/iov.c
>>>>>>>>>> +++ b/drivers/pci/iov.c
>>>>>>>>>> @@ -1013,6 +1013,27 @@ int pci_iov_bus_range(struct pci_bus *bus)
>>>>>>>>>>  	return max ? max - bus->number : 0;
>>>>>>>>>>  }
>>>>>>>>>>  
>>>>>>>>>> +/**
>>>>>>>>>> + * pci_reset_iov_state - reset the state of the IOV capability
>>>>>>>>>> + * @dev: the PCI device
>>>>>>>>>> + */
>>>>>>>>>> +void pci_reset_iov_state(struct pci_dev *dev)
>>>>>>>>>> +{
>>>>>>>>>> +	struct pci_sriov *iov = dev->sriov;
>>>>>>>>>> +
>>>>>>>>>> +	if (!dev->is_physfn)
>>>>>>>>>> +		return;
>>>>>>>>>> +	if (!iov->num_VFs)
>>>>>>>>>> +		return;
>>>>>>>>>> +
>>>>>>>>>> +	sriov_del_vfs(dev);
>>>>>>>>>> +
>>>>>>>>>> +	if (iov->link != dev->devfn)
>>>>>>>>>> +		sysfs_remove_link(&dev->dev.kobj, "dep_link");
>>>>>>>>>> +
>>>>>>>>>> +	iov->num_VFs = 0;
>>>>>>>>>> +}
>>>>>>>>>> +
>>>
>>> Any reason for not using pci_disable_sriov()?
>>
>> The issue with pci_disable_sriov() is that it calls sriov_disable(),
>> which directly uses pci_cfg_access_lock(), leading to deadlock on the
>> FLR path.
>>
> 
> That'll be a problem. Well my main concern is whether the VFs will be reset
> correctly through pci_reset_iov_state() as it lacks the participant of
> PF driver and bios (seems may needed only on powerpc, not sure), which is
> necessary in the enable/disable routine through $pci_dev/sriov_numvfs.
> 
>>>
>>> With the spec the related registers in the SRIOV cap will be reset so
>>> it's ok in general. But for some devices not following the spec like hns3,
>>> some fields like VF enable won't be reset and keep enabled after the FLR.
>>> In this case after the FLR the VF devices in the system has gone but
>>> the state of the PF SRIOV cap leaves uncleared. pci_disable_sriov()
>>> will reset the whole SRIOV cap. It'll also call pcibios_sriov_disable()
>>> to correct handle the VF disabling on some platforms, IIUC.
>>>
>>> Or is it better to use pdev->driver->sriov_configure(pdev,0)?
>>> PF drivers must implement ->sriov_configure() for enabling/disabling
>>> the VF but we totally skip the PF driver here.
>>>
>>> Thanks,
>>> Yicong
>>>
>>>>>>>>>>  /**
>>>>>>>>>>   * pci_enable_sriov - enable the SR-IOV capability
>>>>>>>>>>   * @dev: the PCI device
>>>>>>>>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>>>>>>>>> index 3d2fb394986a..535f19d37e8d 100644
>>>>>>>>>> --- a/drivers/pci/pci.c
>>>>>>>>>> +++ b/drivers/pci/pci.c
>>>>>>>>>> @@ -4694,6 +4694,8 @@ EXPORT_SYMBOL(pci_wait_for_pending_transaction);
>>>>>>>>>>   */
>>>>>>>>>>  int pcie_flr(struct pci_dev *dev)
>>>>>>>>>>  {
>>>>>>>>>> +	pci_reset_iov_state(dev);
>>>>>>>>>> +
>>>>>>>>>>  	if (!pci_wait_for_pending_transaction(dev))
>>>>>>>>>>  		pci_err(dev, "timed out waiting for pending transaction; performing function level reset anyway\n");
>>>>>>>>>>  
>>>>>>>>>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>>>>>>>>>> index 3d60cabde1a1..7bb144fbec76 100644
>>>>>>>>>> --- a/drivers/pci/pci.h
>>>>>>>>>> +++ b/drivers/pci/pci.h
>>>>>>>>>> @@ -480,6 +480,7 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno);
>>>>>>>>>>  resource_size_t pci_sriov_resource_alignment(struct pci_dev *dev, int resno);
>>>>>>>>>>  void pci_restore_iov_state(struct pci_dev *dev);
>>>>>>>>>>  int pci_iov_bus_range(struct pci_bus *bus);
>>>>>>>>>> +void pci_reset_iov_state(struct pci_dev *dev);
>>>>>>>>>>  extern const struct attribute_group sriov_pf_dev_attr_group;
>>>>>>>>>>  extern const struct attribute_group sriov_vf_dev_attr_group;
>>>>>>>>>>  #else
>>>>>>>>>> @@ -501,6 +502,9 @@ static inline int pci_iov_bus_range(struct pci_bus *bus)
>>>>>>>>>>  {
>>>>>>>>>>  	return 0;
>>>>>>>>>>  }
>>>>>>>>>> +static inline void pci_reset_iov_state(struct pci_dev *dev)
>>>>>>>>>> +{
>>>>>>>>>> +}
>>>>>>>>>>  
>>>>>>>>>>  #endif /* CONFIG_PCI_IOV */
>>>> .
>>>>
>> .
>>
> .
> 

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