netdev - Re: [PATCH net-next] ethtool: Fail number of channels change when it conflicts with rxnfc

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Date:   Tue, 1 Nov 2022 09:50:30 -0700
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Jakub Kicinski <kuba@...nel.org>, Gal Pressman <gal@...dia.com>
CC:     "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        "Tariq Toukan" <tariqt@...dia.com>
Subject: Re: [PATCH net-next] ethtool: Fail number of channels change when it
 conflicts with rxnfc



On 10/31/2022 6:23 PM, Jakub Kicinski wrote:
> On Mon, 31 Oct 2022 12:00:16 +0200 Gal Pressman wrote:
>> Similar to what we do with the hash indirection table [1], when network
>> flow classification rules are forwarding traffic to channels greater
>> than the requested number of channels, fail the operation.
>> Without this, traffic could be directed to channels which no longer
>> exist (dropped) after changing number of channels.
>>
>> [1] commit d4ab4286276f ("ethtool: correctly ensure {GS}CHANNELS doesn't conflict with GS{RXFH}")
> 
> Have you made sure there are no magic encodings of queue numbers this
> would break? I seem to recall some vendors used magic queue values to
> redirect to VFs before TC and switchdev. If that's the case we'd need
> to locate the drivers that do that and flag them so we can enforce this
> only going forward?

I believe these all use the same encoding defined by 
ethtool_get_flow_spec_ring and ethtool_get_flow_spec_vf, at least that's 
what ixgbe uses.

This sets the lower 32 bits as the queue index and the next 8 bits as 
the VF identifier as defined by ETHTOOL_RX_FLOW_SPEC_RING and 
ETHTOOL_RX_FLOW_SPEC_RING_VF.

It looks like this change should just exempt ring_cookie with 
ethtool_get_flow_spec_vf as non-zero?

We maybe ought to mark this whole thing as deprecated now given the 
advances in TC.

Thanks,
Jake