[PATCH] arch: arm64: fix KERNEL_SEGMENT_COUNT error

[Zhaoyang Huang]

On Wed, Apr 29, 2026 at 2:19 PM zhaoyang.huang
<zhaoyang.huang at unisoc.com> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang at unisoc.com>
>
> During debug of a kernel panic, we find that the pte_t of the final
> part of [data, end] segment got overflow to the next page of
> init_pg_end[1] which is the gap page before early_init_stack[2].
> This should be introduced by the KERNEL_SEGMENT_COUNT's value is 5
> which should be 6 as map_segment are called 6 times for the segments
> of (text, stext, rodata, inittext, initdata, data+bss)
>
> [1]
> crash_arm64_v9.0.1> vtop ffffffed00601000
> VIRTUAL           PHYSICAL
> ffffffed00601000  83401000
>
> PAGE DIRECTORY: ffffffecffd62000
>    PGD: ffffffecffd62da0 => 10000000833fb003
>    PMD: ffffff80033fb018 => 10000000833fe003
>    PTE: ffffff80033fe008 => 68000083401f03
>   PAGE: 83401000
>
>      PTE        PHYSICAL  FLAGS
> 68000083401f03  83401000  (VALID|SHARED|AF|NG|PXN|UXN)
>
>       PAGE       PHYSICAL      MAPPING       INDEX CNT FLAGS
> fffffffec00d0040 83401000                0        0  1 4000 reserved
>
> [2]
> ffffffed002c8000 (r) __pi__data
> ffffffed0054e000 (d) __pi___bss_start
> ffffffed005f5000 (b) __pi_init_pg_dir
> ffffffed005fe000 (b) __pi_init_pg_end
> ffffffed005ff000 (B) early_init_stack
> ffffffed00608000 (b) __pi__end
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang at unisoc.com>
> ---
>  arch/arm64/include/asm/kernel-pgtable.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index 74a4f738c5f5..14dd1c52552a 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -64,8 +64,8 @@
>  #define INIT_IDMAP_FDT_PAGES   (EARLY_PAGES(INIT_IDMAP_PGTABLE_LEVELS, 0UL, UL(MAX_FDT_SIZE), 1) - 1)
>  #define INIT_IDMAP_FDT_SIZE    ((INIT_IDMAP_FDT_PAGES + EARLY_IDMAP_EXTRA_FDT_PAGES) * PAGE_SIZE)
>
> -/* The number of segments in the kernel image (text, rodata, inittext, initdata, data+bss) */
> -#define KERNEL_SEGMENT_COUNT   5
> +/* The number of segments in the kernel image (text, stext, rodata, inittext, initdata, data+bss) */
> +#define KERNEL_SEGMENT_COUNT   6
>
>  #if SWAPPER_BLOCK_SIZE > SEGMENT_ALIGN
>  #define EARLY_SEGMENT_EXTRA_PAGES (KERNEL_SEGMENT_COUNT + 1)
I just noticed that the page just behind init_pg_end which I called as
guard page is designed as early_init_stack in vmlinux.lds.s. That
could explain why I find the strings of aliases within
idreg-override.c present in this page.

ffffffed005fe000 (b) __pi_init_pg_end
...
ffffffed005fec50:  77735f34366d7261 726c3d656876682e   arm64_sw.hvhe=lr
ffffffed005fec60:  00003d633d723d3d 0000000000000000   ==r=c=..........
...
ffffffed005ff000 (B) early_init_stack