[PATCHv3] arch: arm64: fix KERNEL_SEGMENT_COUNT error

[zhaoyang.huang]

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

Fixes: 5973a62efa34 ("arm64: map [_text, _stext) virtual address range non-executable+read-only")
Assisted-by: TRAE: GLM-5.1
Suggested-by: Ard Biesheuvel <ardb at kernel.org>
Signed-off-by: Zhaoyang Huang <zhaoyang.huang at unisoc.com>
---
Patchv2: make the size of vmlinux_reg[] more reasonable
Patchv3: use extra value of 2 to meet the final segments count
---
---
 arch/arm64/include/asm/kernel-pgtable.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 74a4f738c5f5..f6aed326e1ce 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -68,7 +68,9 @@
 #define KERNEL_SEGMENT_COUNT	5
 
 #if SWAPPER_BLOCK_SIZE > SEGMENT_ALIGN
-#define EARLY_SEGMENT_EXTRA_PAGES (KERNEL_SEGMENT_COUNT + 1)
+
+/* [_text, _stext) is mapped separately which consume 1 extra page */
+#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
-- 
2.25.1