Re: [PATCH v2] iov: restore NumVFs register to 0 before return from virtfn_max_buses()

[ethan zhao <ethan.zhao@oracle.com>]

Alex,
On 2015/10/27 23:15, Alexander Duyck wrote:
> On 10/27/2015 02:28 AM, ethan zhao wrote:
>> Alexander,
>> On 2015/10/27 13:48, Alexander Duyck wrote:
>>> On 10/15/2015 10:16 AM, Bjorn Helgaas wrote:
>>>> Hi Ethan,
>>>>
>>>> On Wed, Sep 16, 2015 at 12:19:53PM +0900, Ethan Zhao wrote:
>>>>> After commit 4449f079722c ("PCI: Calculate maximum number of buses
>>>>> required for VFs"),the initial value of NumVFs register was left to
>>>>> non-zero after sriov_init() and no VFs was enabled in device driver.
>>>>> this changed the behaviour of kernel exported by lspci and sysfs etc.
>>>>> so this patch restore the NumVFs register to zero after the
>>>>> calculation of max_VF_buses was done and before return from
>>>>> virtfn_max_buses().
>>>>>
>>>>> Tested on stable 4.1 and passed building on stable 4.3-rc1
>>>>>
>>>>> Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
>>>>> Tested-by: Sriharsha Yadagudde <sriharsha.devdas@oracle.com>
>>>> Can you test the patch below?  I'm trying to avoid touching
>>>> PCI_SRIOV_NUM_VF in more than one place, and I think it's OK to set it
>>>> and test offset/stride at the end, instead of setting NUM_VF to zero,
>>>> testing offset/stride, computing max_bus, then setting NUM_VF to zero
>>>> again.
>>>>
>>>> Bjorn
>>>>
>>>>
>>>> commit 8e20e89658f23b8d16b1e21810e9f63c8625129c
>>>> Author: Bjorn Helgaas <bhelgaas@google.com>
>>>> Date:   Thu Oct 15 11:31:21 2015 -0500
>>>>
>>>>      PCI: Set SR-IOV NumVFs to zero after enumeration
>>>>           The enumeration path should leave NumVFs set to zero. But 
>>>> after
>>>>      4449f079722c ("PCI: Calculate maximum number of buses required 
>>>> for VFs"),
>>>>      we call virtfn_max_buses() in the enumeration path, which 
>>>> changes NumVFs.
>>>>      This NumVFs change is visible via lspci and sysfs until a 
>>>> driver enables
>>>>      SR-IOV.
>>>>           Set NumVFs to zero after virtfn_max_buses() computes the 
>>>> maximum number of
>>>>      buses.
>>>>           Fixes: 4449f079722c ("PCI: Calculate maximum number of 
>>>> buses required for VFs")
>>>>      Based-on-patch-by: Ethan Zhao <ethan.zhao@oracle.com>
>>>>      Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>>>
>>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>> index ee0ebff..0202ab0 100644
>>>> --- a/drivers/pci/iov.c
>>>> +++ b/drivers/pci/iov.c
>>>> @@ -384,7 +384,7 @@ static int sriov_init(struct pci_dev *dev, int 
>>>> pos)
>>>>       int rc;
>>>>       int nres;
>>>>       u32 pgsz;
>>>> -    u16 ctrl, total, offset, stride;
>>>> +    u16 ctrl, total;
>>>>       struct pci_sriov *iov;
>>>>       struct resource *res;
>>>>       struct pci_dev *pdev;
>>>> @@ -414,11 +414,6 @@ static int sriov_init(struct pci_dev *dev, int 
>>>> pos)
>>>>     found:
>>>>       pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
>>>> -    pci_write_config_word(dev, pos + PCI_SRIOV_NUM_VF, 0);
>>>> -    pci_read_config_word(dev, pos + PCI_SRIOV_VF_OFFSET, &offset);
>>>> -    pci_read_config_word(dev, pos + PCI_SRIOV_VF_STRIDE, &stride);
>>>> -    if (!offset || (total > 1 && !stride))
>>>> -        return -EIO;
>>>>         pci_read_config_dword(dev, pos + PCI_SRIOV_SUP_PGSIZE, &pgsz);
>>>>       i = PAGE_SHIFT > 12 ? PAGE_SHIFT - 12 : 0;
>>>> @@ -456,8 +451,6 @@ found:
>>>>       iov->nres = nres;
>>>>       iov->ctrl = ctrl;
>>>>       iov->total_VFs = total;
>>>> -    iov->offset = offset;
>>>> -    iov->stride = stride;
>>>>       iov->pgsz = pgsz;
>>>>       iov->self = dev;
>>>>       pci_read_config_dword(dev, pos + PCI_SRIOV_CAP, &iov->cap);
>>>> @@ -475,6 +468,11 @@ found:
>>>>       dev->sriov = iov;
>>>>       dev->is_physfn = 1;
>>>>       iov->max_VF_buses = virtfn_max_buses(dev);
>>>> +    pci_iov_set_numvfs(dev, 0);
>>>> +    if (!iov->offset || (total > 1 && !iov->stride)) {
>>>> +        rc = -EIO;
>>>> +        goto failed;
>>>> +    }
>>>>         return 0;
>>>
>>> You might want to reorder this a bit.  The problem is offset and 
>>> stride can be 0 if numvfs is 0.  So you should probably test offset 
>>> and stride 
>>  Yes, the spec says "Note: First VF Offset is unused if NumVFs is 0. 
>> If NumVFs is greater than 0, First VF Offset must
>> 25 not be zero. "
>>> first, and then reset numvfs to 0.
>>  Why test it before reset numvfs ?
>
> Because pci_iov_set_numvfs will end up resetting offset and stride 
> based on the values when it writes the 0 into numvfs.  As such 

  Seems virtfn_max_buses() never call pci_iov_set_numvfs() with 0, so no 
need to check it before the last resetting to 0 ?
> testing it after the reset could give you invalid values since offset 
> and stride can be 0 when numvfs is 0.
>
> Actually maybe I will go over this and submit a couple patches 
> myself.  Looking over things it seems like the code has gotten a bit 
> silly since virtfn_max_busses looks like it is iterating over VFs and 
> that doesn't make much sense when offset and stride are both positive 
   so far it works at least. :>

  Thanks,
  Ethan
> values so it should just be a matter of computing the bus of the last VF.
>
> - Alex