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

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Message-ID: <562F1024.70001@gmail.com>
Date:	Mon, 26 Oct 2015 22:48:20 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	Bjorn Helgaas <helgaas@...nel.org>,
	Ethan Zhao <ethan.zhao@...cle.com>
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 10/15/2015 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 
first, and then reset numvfs to 0.

- Alex

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