Hi, Guanyou

Thank you for the patch.

On 4/17/24 19:55, devel-request@lists.crash-utility.osci.io wrote:
> Date: Wed, 17 Apr 2024 19:55:40 +0800
> From: Guanyou Chen<chenguanyou9338@gmail.com>
> Subject: [Crash-utility] [PATCH] arm64: section_size_bits compatible
>       with macro definitions
> To:k-hagio-ab@nec.com,devel@lists.crash-utility.osci.io,      Lianbo
>       <lijiang@redhat.com>
> Message-ID:
>       <CAHS3RMXw5Ya44Nc+fFQqXdwYvHcDnq1RG7-zPpbqTOPoCb0YUw@mail.gmail.com>
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>
> --000000000000492e3b0616498933
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>
> Hi Kazu,
>
> Compatible with google android GKI changes,
> SECTION_SIZE_BITS = 27 when defined 4K_PAGES or 16K_PAGES.
> SECTION_SIZE_BITS = 29 when defined 64K_PAGES.
>
> Link:
> https://lore.kernel.org/lkml/15cf9a2359197fee0168f820c5c904650d07939e.1610146597.git.sudaraja@codeaurora.org
> Link:
> https://lore.kernel.org/all/43843c5e092bfe3ec4c41e3c8c78a7ee35b69bb0.1611206601.git.sudaraja@codeaurora.org
>
> See:
> https://cs.android.com/android/_/android/kernel/common/+/673e9ab6b64f981159aeff3b65675bb7dbedecd8
> Before android-12-gki:
>      crash> help -m | grep section_size_bits
>         section_size_bits: 30
>
> The first PFN error, the physical address should be 0x40000000.
>      crash> kmem -p
>            PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>      ffffffff06e00000 200000000 ffffff80edf4fa12 ffffffff070f3640  1
> 4000000000002000 private
>
> After android-12-gki:
>      crash> help -m | grep section
>         section_size_bits: 27
>
>      crash> kmem -p
>            PAGE        PHYSICAL      MAPPING       INDEX CNT FLAGS
>      fffffffeffe00000  40000000                0        0  1 1000 reserved

The macro SECTION_SIZE_BITS has changed since kernel version 5.12, see:

kernel commit: f0b13ee23241 ("arm64/sparsemem: reduce SECTION_SIZE_BITS")

crash commit: 8246dce99dd2 ("arm64: Update SECTION_SIZE_BITS for kernels
 >= 5.12")


And later kernel exported the SECTION_SIZE_BITS in kernel version
v5.13-rc7~20^2~10:

kernel commit: 4f5aecdff25f ("crash_core, vmcoreinfo: append
'SECTION_SIZE_BITS' to vmcoreinfo")


Crash-utility also reads the value from vmcoreinfo as below:

         if (arm64_get_vmcoreinfo(&machdep->section_size_bits,
"NUMBER(SECTION_SIZE_BITS)", NUM_DEC))

So I'm wondering if this issue occurs on older kernels(e.g. 5.12 or
earlier), and probably introduced some latest kernel patches(such as
kernel commit f0b13ee23241) to the old kernel. Just want to confirm this.


> Signed-off-by: chenguanyou<chenguanyou@xiaomi.com>
> ---
>   arm64.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arm64.c b/arm64.c
> index e36c723..50e22ea 100644
> --- a/arm64.c
> +++ b/arm64.c
> @@ -1629,7 +1629,16 @@ arm64_get_section_size_bits(void)
>              if ((ret = get_kernel_config("CONFIG_HOTPLUG_SIZE_BITS",
> &string)) == IKCONFIG_STR)
>                  machdep->section_size_bits = atol(string);
>          }
> -   }
> +
> +       // arm64: reduce section size for sparsemem
> +       if ((ret = get_kernel_config("CONFIG_ARM64_4K_PAGES", NULL)) ==
> IKCONFIG_Y
> +               || (ret = get_kernel_config("CONFIG_ARM64_16K_PAGES",
> NULL)) == IKCONFIG_Y)
> +           machdep->section_size_bits = _SECTION_SIZE_BITS_5_12;
> +       // arm64/sparsemem: reduce SECTION_SIZE_BITS
> +       else if ((ret = get_kernel_config("CONFIG_ARM64_64K_PAGES", NULL))
> == IKCONFIG_Y)
> +           machdep->section_size_bits = _SECTION_SIZE_BITS_5_12_64K;
> +
> +    }

The IKCONFIG may not be set for many distributions, but this looks like
it works well in your cases.


Thanks.

Lianbo

>      if (CRASHDEBUG(1))
>          fprintf(fp, "SECTION_SIZE_BITS: %ld\n", machdep->section_size_bits);
> -- 2.39.0