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

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Message-ID: <8d36d695-dd66-c21f-f49e-f6dc3dbdfc5a@ti.com>
Date:   Tue, 27 Aug 2019 15:25:06 -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"

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.

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.

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 */
>>>
>>