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Date:   Wed, 19 Oct 2022 11:04:33 -0400
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Subject: Re: [PATCH net] net: fman: Use physical address for userspace
 interfaces
Content-Language: en-US
To:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Madalin Bucur <madalin.bucur@nxp.com>
Cc:     Andrew Lunn <andrew@lunn.ch>, Andrew Davis <afd@ti.com>,
        "David S . Miller" <davem@davemloft.net>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Camelia Alexandra Groza <camelia.groza@nxp.com>
References: <20221017162807.1692691-1-sean.anderson@seco.com>
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From:   Sean Anderson <sean.anderson@seco.com>
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On 10/19/22 02:46, Geert Uytterhoeven wrote:
> Hi Madalin,
> 
> On Wed, Oct 19, 2022 at 7:20 AM Madalin Bucur <madalin.bucur@nxp.com> wrote:
>>> -----Original Message-----
>>> From: Sean Anderson <sean.anderson@seco.com>
>>> Sent: 19 October 2022 00:47
>>> To: Andrew Lunn <andrew@lunn.ch>; Andrew Davis <afd@ti.com>
>>> Cc: David S . Miller <davem@davemloft.net>; netdev@vger.kernel.org;
>>> linux-kernel@vger.kernel.org; Madalin Bucur <madalin.bucur@nxp.com>;
>>> Jakub Kicinski <kuba@kernel.org>; Eric Dumazet <edumazet@google.com>;
>>> Paolo Abeni <pabeni@redhat.com>; Camelia Alexandra Groza
>>> <camelia.groza@nxp.com>; Geert Uytterhoeven <geert@linux-m68k.org>
>>> Subject: Re: [PATCH net] net: fman: Use physical address for userspace
>>> interfaces
>>>
>>>
>>>
>>> On 10/18/22 5:39 PM, Andrew Lunn wrote:
>>>> On Tue, Oct 18, 2022 at 01:33:55PM -0500, Andrew Davis wrote:
>>>>> On 10/18/22 12:37 PM, Sean Anderson wrote:
>>>>>> Hi Andrew,
>>>>>>
>>>>>> On 10/18/22 1:22 PM, Andrew Lunn wrote:
>>>>>>> On Mon, Oct 17, 2022 at 12:28:06PM -0400, Sean Anderson wrote:
>>>>>>>> For whatever reason, the address of the MAC is exposed to
>>> userspace in
>>>>>>>> several places. We need to use the physical address for this
>>> purpose to
>>>>>>>> avoid leaking information about the kernel's memory layout, and
>>> to keep
>>>>>>>> backwards compatibility.
>>>>>>>
>>>>>>> How does this keep backwards compatibility? Whatever is in user
>>> space
>>>>>>> using this virtual address expects a virtual address. If it now
>>> gets a
>>>>>>> physical address it will probably do the wrong thing. Unless there
>>> is
>>>>>>> a one to one mapping, and you are exposing virtual addresses
>>> anyway.
>>>>>>>
>>>>>>> If you are going to break backwards compatibility Maybe it would
>>> be
>>>>>>> better to return 0xdeadbeef? Or 0?
>>>>>>>
>>>>>>>          Andrew
>>>>>>>
>>>>>>
>>>>>> The fixed commit was added in v6.1-rc1 and switched from physical to
>>>>>> virtual. So this is effectively a partial revert to the previous
>>>>>> behavior (but keeping the other changes). See [1] for discussion.
>>>>
>>>> Please don't assume a reviewer has seen the previous
>>>> discussion. Include the background in the commit message to help such
>>>> reviewers.
> 
>>>>> I see it asked in that thread, but not answered. Why are you exposing
>>>>> "physical" addresses to userspace? There should be no reason for that.
>>>>
>>>> I don't see anything about needing physical or virtual address in the
>>>> discussion, or i've missed it.
>>>
>>> Well, Madalin originally added this, so perhaps she has some insight.
>>>
>>> I have no idea why we set the IFMAP stuff, since that seems like it's for
>>> PCMCIA. Not sure about sysfs either.
>>>
>>>> If nobody knows why it is needed, either use an obfusticated value, or
>>>> remove it all together. If somebody/something does need it, they will
>>>> report the regression.
>>>
>>> I'd rather apply this (or v2 of this) and then remove the "feature" in
>>> follow-up.
>>>
>>> --Sean
>>
>>
>> root@localhost:~# grep 1ae /etc/udev/rules.d/72-fsl-dpaa-persistent-networking.rules
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae0000", NAME="fm1-mac1"
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae2000", NAME="fm1-mac2"
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae4000", NAME="fm1-mac3"
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae6000", NAME="fm1-mac4"
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1ae8000", NAME="fm1-mac5"
>> SUBSYSTEM=="net", DRIVERS=="fsl_dpa*", ATTR{device_addr}=="1aea000", NAME="fm1-mac6"
> 
> So you rely on the physical address.
> It's a pity this uses a custom sysfs file.
> Can't you obtain this information some other way?
> Anyway, as this is in use, it became part of the ABI.

In my udev rules I use ID_PATH. Since this is a devicetree platform, the path name includes
the device address by convention.

--Sean

>> root@localhost:~# grep 1ae  /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@*/net/fm1-mac*/device_addr
>> /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@2/net/fm1-mac3/device_addr:1ae4000
>> /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@3/net/fm1-mac4/device_addr:1ae6000
>> /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@4/net/fm1-mac5/device_addr:1ae8000
>> /sys/devices/platform/soc/soc:fsl,dpaa/soc:fsl,dpaa:ethernet@5/net/fm1-mac6/device_addr:1aea000
> 
> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                  -- Linus Torvalds