linux-kernel - Re: [PATCH] arm: remove [_text, _stext) from kernel code resource

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Message-ID: <YbB+O80Th2QI8sTl@kernel.org>
Date:   Wed, 8 Dec 2021 11:43:23 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Cc:     akpm@...ux-foundation.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org, linux@...linux.org.uk,
        linux@...ck-us.net, matthias.bgg@...il.com,
        rmk+kernel@...linux.org.uk, wangkefeng.wang@...wei.com,
        yj.chiang@...iatek.com
Subject: Re: [PATCH] arm: remove [_text, _stext) from kernel code resource

On Wed, Dec 08, 2021 at 10:26:23AM +0800, Mark-PK Tsai wrote:
> > On Fri, Dec 03, 2021 at 10:14:16PM +0800, Mark-PK Tsai wrote:
> > > Remove the [_text, _stext) from Kernel Code.
> > > Although there are some startup code in head.text, they
> > > are freed to the buddy system after kernel boot.
> >
> > Hmm, I don't see it is being freed anywhere. Can you elaborate when and how
> > the range [_text, _stext) is freed?
> 
> arm_memblock_init() reserve [KERNEL_START, KERNEL_END) which are defined as following.
> 
> #define KERNEL_START            _stext
> #define KERNEL_END              _end
> 
> free_low_memory_core_early() free all the non-reserved range in lowmem,
> so the range [_text, _stext) is also freed here.

Right, I've misread KERNEL_START as if it was _text...
 
> >
> > > And we have memory protection mechanism use this
> > > which have false alarm when some other IPs doing dma
> > > if the dma page frame is in the [_text, _stext).
> > >
> > > Below are my iomem resource and reserved memory information:
> > > console:/ # grep Kernel /proc/iomem
> > >   20208000-219fffff : Kernel code
> > >   21b00000-21c2e76f : Kernel data
> > >
> > > console:/ # cat /sys/kernel/debug/memblock/reserved
> > > 0: 0x20201000..0x20207fff
> > > 1: 0x20300000..0x21c2e76f
> >
> > What are the addresses of _text and _stext in your configuration?
> 
> va	 pa
> c0008000 20208000 _text
> c0100000 20300000 _stext
> 
> >
> > What these dumps are supposed to show here?
> >
> 
> Below is the dump info after applied this patch.
> 
> console:/ # grep Kernel /proc/iomem
>   20300000-219fffff : Kernel code
>   21b00000-21c2e76f : Kernel data
> 
> console:/ # cat /sys/kernel/debug/memblock/reserved
> 0: 0x20201000..0x20207fff
> 1: 0x20300000..0x21c2e76f
> 
> The difference is that Kernel Code resource match the reserved memblock 1
> which is reserved in arm_memblock_init().

For that I'd extend the reservation in arm_memblock_init() to include
[_text, _stext). 

Even if the code there is not needed after init, at least we'll keep this
consistent with other architectures.
 

-- 
Sincerely yours,
Mike.