linux-kernel - Re: [PATCH] ARM: mmu: fix access to illegal address when using earlycon & memblock=debug

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Message-ID: <ecabcfa6-7408-d10b-7d88-b1a202b2a90d@allwinnertech.com>
Date:   Fri, 17 Jun 2022 21:30:57 +0800
From:   Victor Hassan <victor@...winnertech.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     linux@...linux.org.uk, rmk+kernel@...linux.org.uk,
        yanfei.xu@...driver.com, ardb@...nel.org, tglx@...utronix.de,
        mirq-linux@...e.qmqm.pl, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: mmu: fix access to illegal address when using
 earlycon & memblock=debug

On 4/18/2022 11:08 PM, Victor Hassan wrote:
> On 18/04/2022 07:21, Linus Walleij wrote:
>> On Wed, Mar 16, 2022 at 3:33 AM Victor Hassan 
>> <victor@...winnertech.com> wrote:
>>
>>> earlycon uses fixmap to create a memory map,
>>> So we need to close earlycon before closing fixmap,
>>> otherwise printk will access illegal addresses.
>>> After creating a new memory map, we open earlycon again.
>>>
>>> Signed-off-by: Victor Hassan <victor@...winnertech.com>
>>
>> I think noone really noticed this because everyone on Arm systems
>> use CONFIG_DEBUG_LL, and that makes printascii hammer out
>> stuff on the console very early, it even accounts for whether we have
>> MMU on or not.
>>
> Hi Linus,
> Thank you for the reply. I used earlycon, in early_fixmap_shutdown, the 
> base address of earlycon is in the critical stage of release and 
> reassignment, so early_fixmap_shutdown -> create_mapping should not call 
> earlycon in this process, and create_mapping has a lot of conditions 
> that trigger print, memblock=debug just makes it easier to expose problems.
> 
>> How are you using this on Arm even? What system and what serial
>> driver?
> I'm using serial driver 8250 on arm32, with cmdline: memblock=debug.
> CONFIG_SERIAL_8250=y
> CONFIG_SERIAL_8520_CONSOLE=y
>>
>> That said, it looks correct.
>> Acked-by: Linus Walleij <linus.walleij@...aro.org>

Hi Linus,
Sorry to disturb. Is there any question about this issue? Thank you :)