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

Ard Biesheuvel
2026-04-30T08:00:05Z

On Thu, 30 Apr 2026, at 03:56, Zhaoyang Huang wrote:
> On Thu, Apr 30, 2026 at 9:29 AM Zhaoyang Huang <huangzhaoyang@gmail.com> wrote:
>>
>> On Wed, Apr 29, 2026 at 5:28 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>> >
>> > 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)
>> Thanks for the comment. This makes sense since KERNEL_SEGMENT_COUNT is
>> also used for defining vmlinux_seg[] in declare_kernel_vmas.
> Is the following fix more reasonable, since it makes both map_segment
> and declare_kernel_vmas compatible with the value 6?
>

No, please fix this as I suggested.