Messages in this thread | | | From | Mark-PK Tsai <> | Subject | Re: [PATCH] arm: remove [_text, _stext) from kernel code resource | Date | Wed, 8 Dec 2021 18:22:37 +0800 |
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> 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. >
Extending the reservation in arm_memblock_init() will consume up to SECTION_SIZE memory for SECTION_SIZE alignment when CONFIG_STRICT_KERNEL_RWX=y. So we really don't want to extend the reservation because it affect the low RAM devices.
And arm64_memblock_init() also reserve [_stext, _end) in the recent kernel.
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