linux-kernel - Re: [PATCH] PCI: IOV: reread SRIOV_NUM

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Date:	Wed, 7 Oct 2015 14:29:40 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Ben Shelton <benjamin.h.shelton@...el.com>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: IOV: reread SRIOV_NUM_VF after enabling ARI

Hi Ben,

On Fri, Sep 11, 2015 at 04:55:00PM -0500, Ben Shelton wrote:
> For some SR-IOV devices, the number of available virtual functions
> increases after enabling ARI.  Currently, SRIOV_NUM_VF is read and saved
> off before the ARI control bit is enabled.  This causes an issue when VFs
> are enabled.
> 
> At device init, SRIOV_INITIAL_VF and SRIOV_NUM_VF are specified to contain
> the number of available VFs for the device.  sriov_enable() does a sanity
> check that PCI_SRIOV_INITIAL_VF is not greater than iov->total_VFs, the
> saved-off value of SRIOV_NUM_VF.  Since the value of both SRIOV_INITIAL_VF
> and SRIOV_NUM_VF has increased after enabling the ARI bit, the check fails,
> and the VFs cannot be enabled.
> 
> To fix the issue, after ARI is enabled for a device, reread SRIOV_NUM_VF.
> 
> Signed-off-by: Ben Shelton <benjamin.h.shelton@...el.com>
> ---
>  drivers/pci/iov.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index ee0ebff..88b1959 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -388,6 +388,7 @@ static int sriov_init(struct pci_dev *dev, int pos)
>  	struct pci_sriov *iov;
>  	struct resource *res;
>  	struct pci_dev *pdev;
> +	bool total_needs_reread = false;
>  
>  	if (pci_pcie_type(dev) != PCI_EXP_TYPE_RC_END &&
>  	    pci_pcie_type(dev) != PCI_EXP_TYPE_ENDPOINT)
> @@ -409,12 +410,18 @@ static int sriov_init(struct pci_dev *dev, int pos)
>  			goto found;
>  
>  	pdev = NULL;
> -	if (pci_ari_enabled(dev->bus))
> +	if (pci_ari_enabled(dev->bus)) {
>  		ctrl |= PCI_SRIOV_CTRL_ARI;
> +		total_needs_reread = true;
> +	}
>  
>  found:
>  	pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
>  	pci_write_config_word(dev, pos + PCI_SRIOV_NUM_VF, 0);
> +
> +	if (total_needs_reread)
> +		pci_read_config_word(dev, pos + PCI_SRIOV_TOTAL_VF, &total);

Can we just *move* the PCI_SRIOV_TOTAL_VF read from its original
location and do it unconditionally here?  I don't think we use "total"
for anything in the interim, and it'd be nice if we could do this
without the "total_needs_reread" flag.

>  	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))
> -- 
> 1.9.5
> 
> --
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