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 <kernelf...@gmail.com>
> Cc: Bhupesh Sharma <bhupesh.sha...@linaro.org>
> Cc: Kazuhito Hagio <k-ha...@ab.jp.nec.com>
> Cc: Dave Young <dyo...@redhat.com>
> Cc: Baoquan He <b...@redhat.com>
> Cc: Boris Petkov <b...@alien8.de>
> Cc: Ingo Molnar <mi...@kernel.org>
> Cc: Thomas Gleixner <t...@linutronix.de>
> Cc: James Morse <james.mo...@arm.com>
> Cc: Mark Rutland <mark.rutl...@arm.com>
> Cc: Will Deacon <w...@kernel.org>
> Cc: Catalin Marinas <catalin.mari...@arm.com>
> Cc: Michael Ellerman <m...@ellerman.id.au>
> Cc: Paul Mackerras <pau...@samba.org>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Cc: Dave Anderson <ander...@redhat.com>
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-ker...@vger.kernel.org
> Cc: ke...@lists.infradead.org
> Cc: x...@kernel.org
> Cc: linux-arm-ker...@lists.infradead.org
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 <b...@redhat.com>
> ---
> 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
>
