linux-kernel - Re: [PATCH v2] iov: restore NumVFs register to 0 before return from virtfn_max

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Date:	Tue, 27 Oct 2015 08:15:30 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	ethan zhao <ethan.zhao@...cle.com>,
	Bjorn Helgaas <helgaas@...nel.org>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] iov: restore NumVFs register to 0 before return from
 virtfn_max_buses()

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@...cle.com>
>>>> Tested-by: Sriharsha Yadagudde <sriharsha.devdas@...cle.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@...gle.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@...cle.com>
>>>      Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.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 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 values so it 
should just be a matter of computing the bus of the last VF.

- Alex
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