Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo

[Baoquan He]

On 06/08/21 at 06:33am, Pingfan Liu wrote:
> As mentioned in kernel commit 1d50e5d0c505 ("crash_core, vmcoreinfo:
> Append 'MAX_PHYSMEM_BITS' to vmcoreinfo"), SECTION_SIZE_BITS in the
> formula:
>     #define SECTIONS_SHIFT    (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
> 
> Besides SECTIONS_SHIFT, SECTION_SIZE_BITS is also used to calculate
> PAGES_PER_SECTION in makedumpfile just like kernel.
> 
> Unfortunately, this arch-dependent macro SECTION_SIZE_BITS changes, e.g.
> recently in kernel commit f0b13ee23241 ("arm64/sparsemem: reduce
> SECTION_SIZE_BITS"). But user space wants a stable interface to get this
> info. Such info is impossible to be deduced from a crashdump vmcore.
> Hence append SECTION_SIZE_BITS to vmcoreinfo.

> 
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> Cc: Bhupesh Sharma <bhupesh.sharma@xxxxxxxxxx>
> Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
> Cc: Dave Young <dyoung@xxxxxxxxxx>
> Cc: Baoquan He <bhe@xxxxxxxxxx>
> Cc: Boris Petkov <bp@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: James Morse <james.morse@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> Cc: Dave Anderson <anderson@xxxxxxxxxx>
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: kexec@xxxxxxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx


Add the discussion of the original thread in kexec ML for reference:
http://lists.infradead.org/pipermail/kexec/2021-June/022676.html

This looks good to me.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

> ---
>  kernel/crash_core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 825284baaf46..684a6061a13a 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_init(void)
>  	VMCOREINFO_LENGTH(mem_section, NR_SECTION_ROOTS);
>  	VMCOREINFO_STRUCT_SIZE(mem_section);
>  	VMCOREINFO_OFFSET(mem_section, section_mem_map);
> +	VMCOREINFO_NUMBER(SECTION_SIZE_BITS);
>  	VMCOREINFO_NUMBER(MAX_PHYSMEM_BITS);
>  #endif
>  	VMCOREINFO_STRUCT_SIZE(page);
> -- 
> 2.29.2
>