linux-kernel - Re: [PATCH] rpmsg: virtio_rpmsg

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Date:   Tue, 27 Aug 2019 17:17:28 -0500
From:   Suman Anna <s-anna@...com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
CC:     <linux-remoteproc@...r.kernel.org>,
        Loic Pallardy <loic.pallardy@...com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] rpmsg: virtio_rpmsg_bus: replace "%p" with "%pK"

On 8/27/19 5:15 PM, Suman Anna wrote:
> On 8/27/19 5:07 PM, Bjorn Andersson wrote:
>> On Tue 27 Aug 13:25 PDT 2019, Suman Anna wrote:
>>
>>> Hi Bjorn,
>>>
>>> On 8/27/19 12:10 AM, Bjorn Andersson wrote:
>>>> On Fri 09 Aug 13:25 PDT 2019, Suman Anna wrote:
>>>>
>>>>> Hi Bjorn,
>>>>>
>>>>
>>>> Hi Suman
>>>>
>>>>> On 10/23/18 8:19 PM, Suman Anna wrote:
>>>>>> The virtio_rpmsg_bus driver uses the "%p" format-specifier for
>>>>>> printing the vring buffer address. This prints only a hashed
>>>>>> pointer even for previliged users. Use "%pK" instead so that
>>>>>> the address can be printed during debug using kptr_restrict
>>>>>> sysctl.
>>>>>
>>>>> Seems to have been lost among the patches, can you pick up this trivial
>>>>> patch for 5.4? Should apply cleanly on the latest HEAD as well.
>>>>>
>>>>
>>>> I share Andrew's question regarding what benefit you have from knowing
>>>> this value. Should we not just remove the va from the print? Or do you
>>>> actually have a use case for it?.
>>>
>>> I mainly use it during debug when comparing against kernel_page_tables
>>> and vmallocinfo. The pools that we use are not always guaranteed to be
>>> from linear memory, and behavior changes when using with CMA or DMA pools.
>>>
>>
>> Thanks Suman. It seems to me that there's room for improvement to aid
>> this kind of debugging. But your usecase seems reasonable, so I'm
>> merging the patch.
> 
> Thanks Bjorn.

Btw, looks like you applied the patch against rproc-next instead of
rpmsg-next.

regards
Suman

> 
>>
>>> Note that usage of %pK does not leak the addresses automatically, but
>>> atleast enables me to get the values when needed. The changes also bring
>>> the usage in rpmsg core in sync with the remoteproc core.
>>>
>>
>> Sounds like shouldn't have merged them in remoteproc then ;P
> 
> Slightly different reasoning looking at the commit, it was probably when
> %p was leaking the addresses.
> 
> regards
> Suman
> 
>>
>> Thanks,
>> Bjorn
>>
>>> regards
>>> Suman
>>>
>>>>
>>>> Regards,
>>>> Bjorn
>>>>
>>>>> regards
>>>>> Suman
>>>>>
>>>>>>
>>>>>> Signed-off-by: Suman Anna <s-anna@...com>
>>>>>> ---
>>>>>>  drivers/rpmsg/virtio_rpmsg_bus.c | 2 +-
>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>>> index f29dee731026..1345f373a1a0 100644
>>>>>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
>>>>>> @@ -950,7 +950,7 @@ static int rpmsg_probe(struct virtio_device *vdev)
>>>>>>  		goto vqs_del;
>>>>>>  	}
>>>>>>  
>>>>>> -	dev_dbg(&vdev->dev, "buffers: va %p, dma %pad\n",
>>>>>> +	dev_dbg(&vdev->dev, "buffers: va %pK, dma %pad\n",
>>>>>>  		bufs_va, &vrp->bufs_dma);
>>>>>>  
>>>>>>  	/* half of the buffers is dedicated for RX */
>>>>>>
>>>>>
>>>
>