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 17:28:38 +0800
From:	ethan zhao <ethan.zhao@...cle.com>
To:	Alexander Duyck <alexander.duyck@...il.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()

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 ?

Thanks,
Ethan
>
> - Alex
>

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