linux-kernel - Re: [PATCH v7 3/4] fpga: dfl: add basic support for DFHv1

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Date:   Sat, 31 Dec 2022 12:46:28 -0800 (PST)
From:   matthew.gerlach@...ux.intel.com
To:     Xu Yilun <yilun.xu@...el.com>
cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        hao.wu@...el.com, russell.h.weight@...el.com,
        basheer.ahmed.muddebihal@...el.com, trix@...hat.com,
        mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        tianfei.zhang@...el.com, corbet@....net,
        gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
        jirislaby@...nel.org, geert+renesas@...der.be,
        niklas.soderlund+renesas@...natech.se, macro@...am.me.uk,
        johan@...nel.org, lukas@...ner.de, ilpo.jarvinen@...ux.intel.com,
        marpagan@...hat.com, bagasdotme@...il.com
Subject: Re: [PATCH v7 3/4] fpga: dfl: add basic support for DFHv1



On Mon, 26 Dec 2022, Xu Yilun wrote:

> On 2022-12-21 at 11:14:59 -0800, matthew.gerlach@...ux.intel.com wrote:
>>
>>
>> On Tue, 20 Dec 2022, Andy Shevchenko wrote:
>>
>>> On Tue, Dec 20, 2022 at 08:36:51AM -0800, matthew.gerlach@...ux.intel.com wrote:
>>>> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>>>
>>>> Version 1 of the Device Feature Header (DFH) definition adds
>>>> functionality to the DFL bus.
>>>>
>>>> A DFHv1 header may have one or more parameter blocks that
>>>> further describes the HW to SW.  Add support to the DFL bus
>>>> to parse the MSI-X parameter.
>>>>
>>>> The location of a feature's register set is explicitly
>>>> described in DFHv1 and can be relative to the base of the DFHv1
>>>> or an absolute address.  Parse the location and pass the information
>>>> to DFL driver.
>>>
>>> ...
>>>
>>>> +/**
>>>> + * dfh_find_param() - find data for the given parameter id
>>>> + * @dfl_dev: dfl device
>>>> + * @param: id of dfl parameter
>>>> + *
>>>> + * Return: pointer to parameter header on success, NULL otherwise.
>>>
>>> header is a bit confusing here, does it mean we give and ID and we got
>>> something more than just a data as summary above suggests?
>>
>> Yes, the summary is not correct.  It should say "find the parameter block
>> for the given parameter id".
>>
>>>
>>> In such case summary and this text should clarify what exactly we get
>>> and layout of the data. Since this is a pointer, who is responsible of
>>> checking out-of-boundary accesses? For instance, if the parameters are
>>> variadic by length the length should be returned as well. Otherwise it
>>> should be specified as a constant somewhere, right?
>>
>> The parameter header has the next/size field; so the caller of
>> dfh_find_param should perform boundary checking as part of interpreting the
>> parameter data.  I think a function to perform this checking and data
>> interpretation would help here.
>
> It is better the DFL core provides the size of the parameter block, just
> in this API. It provides the pointer and should be ensured the memory
> for the pointer be correctly understood.

Ok, how about the following API for dfh_find_param?

/**
  * dfh_find_param() - find parameter block for the given parameter id
  * @dfl_dev: dfl device
  * @param_id: id of dfl parameter
  * @pver: destination to store parameter version
  * @pcount: destination to store size of parameter data in u64 bit words
  *
  * Return: pointer to start of parameter data, PTR_ERR otherwise.
  */
void *dfh_find_param(struct dfl_device *dfl_dev, int param_id, unsigned 
*pver, unsigned *pcount)


>
>>
>>>
>>>> + */
>>>> +u64 *dfh_find_param(struct dfl_device *dfl_dev, int param_id)
>>>> +{
>>>> +	return find_param(dfl_dev->params, dfl_dev->param_size, param_id);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(dfh_find_param);
>>>
>>> ...
>>>
>>>> +	finfo = kzalloc(sizeof(*finfo) + dfh_psize, GFP_KERNEL);
>>>
>>> It sounds like a candidate for struct_size() from overflow.h.
>>> I.o.w. check that header and come up with the best what can
>>> suit your case.
>>
>> 	finfo = kzalloc(struct_size(finfo, params, dfh_psize/sizeof(u64)),
>> GFP_KERNEL);
>>
>> Does seem better.
>
> How about we change the dfh_get_psize() to like dfh_get_pcount(), so we
> don't have to multiply & divide back and forth.

We need the size in bytes for calls to kmemdup, devm_kmemdup, and 
memcpy_fromio, but we only need to divide once here.


>
> Or we just use size_add()?

I think using struct_size is better because the params member 
of struct dfl_feature_info is a trailing flexible array.

Thanks for the feedback,
Matthew


>
> Thanks,
> Yilun
>
>>
>> Thanks for the suggestion,
>> Matthew Gerlach
>>
>>
>>>
>>>>  	if (!finfo)
>>>>  		return -ENOMEM;
>>>
>>> --
>>> With Best Regards,
>>> Andy Shevchenko
>>>
>>>
>>>
>