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

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Date:   Wed, 8 Dec 2021 10:26:23 +0800
From:   Mark-PK Tsai <mark-pk.tsai@...iatek.com>
To:     <rppt@...nel.org>
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>, <mark-pk.tsai@...iatek.com>,
        <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 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.

>
> > 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().

>
> > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@...iatek.com>
> > ---
> >  arch/arm/kernel/setup.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> > index 284a80c0b6e1..85ffc9501e38 100644
> > --- a/arch/arm/kernel/setup.c
> > +++ b/arch/arm/kernel/setup.c
> > @@ -851,7 +851,7 @@ static void __init request_standard_resources(const struct machine_desc *mdesc)
> >  	struct resource *res;
> >  	u64 i;
> >
> > -	kernel_code.start   = virt_to_phys(_text);
> > +	kernel_code.start   = virt_to_phys(_stext);
> >  	kernel_code.end     = virt_to_phys(__init_begin - 1);
> >  	kernel_data.start   = virt_to_phys(_sdata);
> >  	kernel_data.end     = virt_to_phys(_end - 1);
> > --
> > 2.18.0
> >
>
> --
> Sincerely yours,
> Mike.