netdev - Re: [PATCH net] net: Disable NETIF_F_HW_TLS_TX when HW

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Date:   Thu, 5 Nov 2020 15:22:53 +0200
From:   Tariq Toukan <ttoukan.linux@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>,
        Moshe Shemesh <moshe@...dia.com>,
        Boris Pismenny <borisp@...dia.com>
Subject: Re: [PATCH net] net: Disable NETIF_F_HW_TLS_TX when HW_CSUM is
 disabled



On 11/4/2020 11:25 PM, Jakub Kicinski wrote:
> On Wed,  4 Nov 2020 12:21:41 +0200 Tariq Toukan wrote:
>> With NETIF_F_HW_TLS_TX packets are encrypted in HW. This cannot be
>> logically done when HW_CSUM offload is off.
> 
> Right. Do you expect drivers to nack clearing NETIF_F_HW_TLS_TX when
> there are active connections, then?  I don't think NFP does.  We either
> gotta return -EBUSY when there are offloaded connections, or at least
> clearly document the expected behavior.
> 

As I see from code, today drivers and TLS stack allow clearing 
NETIF_F_HW_TLS_TX without doing anything to change behavior in existing 
sockets, so they continue to do HW offload. Only new sockets will be 
affected.
I think the same behavior should apply when NETIF_F_HW_TLS_TX is cleared 
implicitly (due to clearing HW_CSUM).

If the existing behavior is not expected, and we should force fallback 
to SW kTLS for existing sockets, then I think this should be fixed 
independently to this patch, as it introduces no new regression.

What do you think?

>> Fixes: 2342a8512a1e ("net: Add TLS TX offload features")
>> Signed-off-by: Tariq Toukan <tariqt@...dia.com>
>> Reviewed-by: Boris Pismenny <borisp@...dia.com>
> 
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 82dc6b48e45f..5f72ea17d3f7 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -9588,6 +9588,11 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
>>   		}
>>   	}
>>   
>> +	if ((features & NETIF_F_HW_TLS_TX) && !(features & NETIF_F_HW_CSUM)) {
>> +		netdev_dbg(dev, "Dropping TLS TX HW offload feature since no CSUM feature.\n");
>> +		features &= ~NETIF_F_HW_TLS_TX;
>> +	}