linux-kernel - Re: [EXTERNAL] Re: [PATCH net-next,v2] net: mana: Add support for Multi Vports on Bare metal

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Message-ID: <648d56af-ed86-4d45-8e7a-944d1563117c@redhat.com>
Date: Wed, 28 May 2025 08:27:30 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Haiyang Zhang <haiyangz@...rosoft.com>, Simon Horman <horms@...nel.org>
Cc: "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 Dexuan Cui <decui@...rosoft.com>,
 "stephen@...workplumber.org" <stephen@...workplumber.org>,
 KY Srinivasan <kys@...rosoft.com>, Paul Rosswurm <paulros@...rosoft.com>,
 "olaf@...fle.de" <olaf@...fle.de>, "vkuznets@...hat.com"
 <vkuznets@...hat.com>, "davem@...emloft.net" <davem@...emloft.net>,
 "wei.liu@...nel.org" <wei.liu@...nel.org>,
 "edumazet@...gle.com" <edumazet@...gle.com>,
 "kuba@...nel.org" <kuba@...nel.org>, "leon@...nel.org" <leon@...nel.org>,
 Long Li <longli@...rosoft.com>,
 "ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
 "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
 "daniel@...earbox.net" <daniel@...earbox.net>,
 "john.fastabend@...il.com" <john.fastabend@...il.com>,
 "bpf@...r.kernel.org" <bpf@...r.kernel.org>, "ast@...nel.org"
 <ast@...nel.org>, "hawk@...nel.org" <hawk@...nel.org>,
 "tglx@...utronix.de" <tglx@...utronix.de>,
 "shradhagupta@...ux.microsoft.com" <shradhagupta@...ux.microsoft.com>,
 "andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
 Konstantin Taranov <kotaranov@...rosoft.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXTERNAL] Re: [PATCH net-next,v2] net: mana: Add support for
 Multi Vports on Bare metal

On 5/22/25 4:51 PM, Haiyang Zhang wrote:
>> -----Original Message-----
>> From: Paolo Abeni <pabeni@...hat.com>
>> Sent: Thursday, May 22, 2025 9:44 AM
>> To: Simon Horman <horms@...nel.org>; Haiyang Zhang
>> <haiyangz@...rosoft.com>
> 
>>>>>>  static int mana_query_device_cfg(struct mana_context *ac, u32
>>>>> proto_major_ver,
>>>>>>  				 u32 proto_minor_ver, u32 proto_micro_ver,
>>>>>> -				 u16 *max_num_vports)
>>>>>> +				 u16 *max_num_vports, u8 *bm_hostmode)
>>>>>>  {
>>>>>>  	struct gdma_context *gc = ac->gdma_dev->gdma_context;
>>>>>>  	struct mana_query_device_cfg_resp resp = {};
>>>>>> @@ -932,7 +932,7 @@ static int mana_query_device_cfg(struct
>> mana_context
>>>>> *ac, u32 proto_major_ver,
>>>>>>  	mana_gd_init_req_hdr(&req.hdr, MANA_QUERY_DEV_CONFIG,
>>>>>>  			     sizeof(req), sizeof(resp));
>>>>>>
>>>>>> -	req.hdr.resp.msg_version = GDMA_MESSAGE_V2;
>>>>>> +	req.hdr.resp.msg_version = GDMA_MESSAGE_V3;
>>>>>>
>>>>>>  	req.proto_major_ver = proto_major_ver;
>>>>>>  	req.proto_minor_ver = proto_minor_ver;
>>>>>
>>>>>> @@ -956,11 +956,16 @@ static int mana_query_device_cfg(struct
>>>>> mana_context *ac, u32 proto_major_ver,
>>>>>>
>>>>>>  	*max_num_vports = resp.max_num_vports;
>>>>>>
>>>>>> -	if (resp.hdr.response.msg_version == GDMA_MESSAGE_V2)
>>>>>> +	if (resp.hdr.response.msg_version >= GDMA_MESSAGE_V2)
>>>>>>  		gc->adapter_mtu = resp.adapter_mtu;
>>>>>>  	else
>>>>>>  		gc->adapter_mtu = ETH_FRAME_LEN;
>>>>>>
>>>>>> +	if (resp.hdr.response.msg_version >= GDMA_MESSAGE_V3)
>>>>>> +		*bm_hostmode = resp.bm_hostmode;
>>>>>> +	else
>>>>>> +		*bm_hostmode = 0;
>>>>>
>>>>> Hi,
>>>>>
>>>>> Perhaps not strictly related to this patch, but I see
>>>>> that mana_verify_resp_hdr() is called a few lines above.
>>>>> And that verifies a minimum msg_version. But I do not see
>>>>> any verification of the maximum msg_version supported by the code.
>>>>>
>>>>> I am concerned about a hypothetical scenario where, say the as yet
>> unknown
>>>>> version 5 is sent as the version, and the above behaviour is used,
>> while
>>>>> not being correct.
>>>>>
>>>>> Could you shed some light on this?
>>>>>
>>>>
>>>> In driver, we specify the expected reply msg version is v3 here:
>>>> req.hdr.resp.msg_version = GDMA_MESSAGE_V3;
>>>>
>>>> If the HW side is upgraded, it won't send reply msg version higher
>>>> than expected, which may break the driver.
>>>
>>> Thanks,
>>>
>>> If I understand things correctly the HW side will honour the
>>> req.hdr.resp.msg_version and thus the SW won't receive anything
>>> it doesn't expect. Is that right?
>>
>> @Haiyang, if Simon's interpretation is correct, please change the
>> version checking in the driver from:
>>
>> 	if (resp.hdr.response.msg_version >= GDMA_MESSAGE_V3)
>>
>> to
>> 	if (resp.hdr.response.msg_version == GDMA_MESSAGE_V3)
>>
>> As the current code is misleading.
> 
> Simon:
> Yes, you are right. So newer HW can support older driver, and vice
> versa.
> 
> Paolo:
> The MANA protocol doesn't remove any existing fields during upgrades.
> 
> So (resp.hdr.response.msg_version >= GDMA_MESSAGE_V3) will continue
> to work in the future. If we change it to 
> (resp.hdr.response.msg_version == GDMA_MESSAGE_V3), 
> we will have to remember to update it to something like:
> (resp.hdr.response.msg_version >= GDMA_MESSAGE_V3 &&
>  resp.hdr.response.msg_version <= GDMA_MESSAGE_V5), 
> if the version is upgraded to v5 in the future. And keep on updating
> the checks on existing fields every time when the version is
> upgraded.
> 
> So, can I keep the ">=" condition, to avoid future bug if anyone
> forget to update checks on all existing fields?

Ok, thanks for the clarification. fine by me.

/P