linux-kernel - Re: [PATCH] iov: initialize NumVFs register to 0 at the end of sriov

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Message-ID: <20150915161016.GB27964@google.com>
Date:	Tue, 15 Sep 2015 11:10:16 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Ethan Zhao <ethan.zhao@...cle.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iov: initialize NumVFs register to 0 at the end of
 sriov_init()

On Fri, Aug 21, 2015 at 06:51:25PM +0900, Ethan Zhao wrote:
> After commit 4449f079722c ("PCI: Calculate maximum number of buses
> required for VFs"),the initial value of NumVFs register was set 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 initialize the NumVFs register to zero after the
> calculation of max_VF_buses was done.
> 
> Tested on stable 4.1 and passed building on stable 4.2-rc7
> 
> Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com>
> Tested-by: Sriharsha Yadagudde <sriharsha.devdas@...cle.com>
> ---
>  drivers/pci/iov.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index ee0ebff..6969084 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -476,6 +476,7 @@ found:
>  	dev->is_physfn = 1;
>  	iov->max_VF_buses = virtfn_max_buses(dev);
>  
> +	pci_iov_set_numvfs(dev, 0);

I think it would be better to put this in virtfn_max_buses(), where we
clobbered numVFs in the first place.  I'd also read the original value and
restore it, e.g.,

    pci_read_config_word(dev, iov->pos + PCI_SRIOV_NUM_VF, &numvfs);
    for (nr_virtfn = 1; nr_virtfn <= iov->total_VFs; nr_virtfn++) {
      ...
    }
    pci_iov_set_numvfs(dev, numvfs);
    return max;

I know sriov_init() sets numVFs to zero before it calls virtfn_max_buses(),
but why rely on that extra knowledge?

>  	return 0;
>  
>  failed:
> -- 
> 1.8.3.1
> 
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