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

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Message-ID: <20190827220711.GK6167@minitux>
Date:   Tue, 27 Aug 2019 15:07:11 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Suman Anna <s-anna@...com>
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 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.

> 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

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 */
> >>>
> >>
>