Re: [PATCH] arch: arm64: fix KERNEL_SEGMENT_COUNT error

Ard Biesheuvel
2026-04-29T09:28:21Z

Hello Zhaoyang,

On Wed, 29 Apr 2026, at 08:17, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@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@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 think the better fix would be

--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -68,7 +68,7 @@
#define KERNEL_SEGMENT_COUNT 5

#if SWAPPER_BLOCK_SIZE > SEGMENT_ALIGN
-#define EARLY_SEGMENT_EXTRA_PAGES (KERNEL_SEGMENT_COUNT + 1)
+#define EARLY_SEGMENT_EXTRA_PAGES (KERNEL_SEGMENT_COUNT + 2)
/*
* The initial ID map consists of the kernel image, mapped as two separate
* segments, and may appear misaligned wrt the swapper block size. This means

and add a line

Fixes: 5973a62efa34 ("arm64: map [_text, _stext) virtual address range non-executable+read-only")