netdev - Re: [net-next 4/4] i40e: Add a check to see if MFS is set

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Message-ID: <20200421105935.4a92485f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 21 Apr 2020 10:59:35 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:     davem@...emloft.net, Todd Fujinaka <todd.fujinaka@...el.com>,
        netdev@...r.kernel.org, nhorman@...hat.com, sassmann@...hat.com,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Andrew Bowers <andrewx.bowers@...el.com>
Subject: Re: [net-next 4/4] i40e: Add a check to see if MFS is set

On Mon, 20 Apr 2020 18:49:32 -0700 Jeff Kirsher wrote:
> From: Todd Fujinaka <todd.fujinaka@...el.com>
> 
> A customer was chain-booting to provision his systems and one of the
> steps was setting MFS. MFS isn't cleared by normal warm reboots
> (clearing requires a GLOBR) and there was no indication of why Jumbo
> Frame receives were failing.
> 
> Add a warning if MFS is set to anything lower than the default.
> 
> Signed-off-by: Todd Fujinaka <todd.fujinaka@...el.com>
> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index 4c414208a22a..3fdbfede0b87 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -15347,6 +15347,15 @@ static int i40e_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  			i40e_stat_str(&pf->hw, err),
>  			i40e_aq_str(&pf->hw, pf->hw.aq.asq_last_status));
>  
> +	/* make sure the MFS hasn't been set lower than the default */
> +#define MAX_FRAME_SIZE_DEFAULT 0x2600
> +	for (i = 0; i < 4; i++) {

Why is this a loop? AFAICS @i is only used in the warning message

> +		val = ((rd32(&pf->hw, I40E_PRTGL_SAH) & I40E_PRTGL_SAH_MFS_MASK)
> +			>> I40E_PRTGL_SAH_MFS_SHIFT);

outer parens unnecessary

> +		if (val < MAX_FRAME_SIZE_DEFAULT)
> +			dev_warn(&pdev->dev, "MFS for port %x has been set below the default: %x\n", i, val);

Shouldn't you just reset it to default at this point? If the value is
not reset on warm boot this is not really a surprise.

> +	}
> +
>  	/* Add a filter to drop all Flow control frames from any VSI from being
>  	 * transmitted. By doing so we stop a malicious VF from sending out
>  	 * PAUSE or PFC frames and potentially controlling traffic for other