linux-kernel - Re: [PATCH net-next v5 05/14] net: fman: Map the base address once

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Date:   Mon, 17 Oct 2022 11:34:47 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Camelia Groza <camelia.groza@....com>,
        Madalin Bucur <madalin.bucur@....com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH net-next v5 05/14] net: fman: Map the base address once



On 10/17/22 11:15 AM, Geert Uytterhoeven wrote:
> Hi Sean,
> 
> On Sat, Sep 3, 2022 at 12:00 AM Sean Anderson <sean.anderson@...o.com> wrote:
>> We don't need to remap the base address from the resource twice (once in
>> mac_probe() and again in set_fman_mac_params()). We still need the
>> resource to get the end address, but we can use a single function call
>> to get both at once.
>>
>> While we're at it, use platform_get_mem_or_io and devm_request_resource
>> to map the resource. I think this is the more "correct" way to do things
>> here, since we use the pdev resource, instead of creating a new one.
>> It's still a bit tricky, since we need to ensure that the resource is a
>> child of the fman region when it gets requested.
>>
>> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
>> Acked-by: Camelia Groza <camelia.groza@....com>
> 
> Thanks for your patch, which is now commit 262f2b782e255b79
> ("net: fman: Map the base address once") in v6.1-rc1.
> 
>> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth_sysfs.c
>> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth_sysfs.c
>> @@ -18,7 +18,7 @@ static ssize_t dpaa_eth_show_addr(struct device *dev,
>>
>>         if (mac_dev)
>>                 return sprintf(buf, "%llx",
>> -                               (unsigned long long)mac_dev->res->start);
>> +                               (unsigned long long)mac_dev->vaddr);
> 
> On 32-bit:
> 
>     warning: cast from pointer to integer of different size
> [-Wpointer-to-int-cast]
> 
> Obviously you should cast to "uintptr_t" or "unsigned long" instead,
> and change the "%llx" to "%p" or "%lx"...

Isn't there a %px for this purpose?

> However, taking a closer look:
>   1. The old code exposed a physical address to user space, the new
>      code exposes the mapped virtual address.
>      Is that change intentional?

No, this is not intentional. So to make this backwards-compatible, I
suppose I need a virt_to_phys?

>   2. Virtual addresses are useless in user space.
>      Moreover, addresses printed by "%p" are obfuscated, as this is
>      considered a security issue. Likewise for working around this by
>      casting to an integer.

Yes, you're right that this probably shouldn't be exposed to userspace.

> What's the real purpose of dpaa_eth_show_addr()?

I have no idea. This is a question for Madalin.

> Perhaps it should be removed?

That would be reasonable IMO.

--Sean

>>         else
>>                 return sprintf(buf, "none");
>>  }
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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
>