linux-kernel - Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE

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Date:   Tue, 8 Jun 2021 22:24:32 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pingfan Liu <kernelfans@...il.com>
Cc:     Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        akpm@...ux-foundation.org, Kazuhito Hagio <k-hagio@...jp.nec.com>,
        Dave Young <dyoung@...hat.com>, Boris Petkov <bp@...en8.de>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        James Morse <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Dave Anderson <anderson@...hat.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] crash_core, vmcoreinfo: Append 'SECTION_SIZE_BITS' to
 vmcoreinfo

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@...il.com>
> Cc: Bhupesh Sharma <bhupesh.sharma@...aro.org>
> Cc: Kazuhito Hagio <k-hagio@...jp.nec.com>
> Cc: Dave Young <dyoung@...hat.com>
> Cc: Baoquan He <bhe@...hat.com>
> Cc: Boris Petkov <bp@...en8.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: James Morse <james.morse@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Dave Anderson <anderson@...hat.com>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-kernel@...r.kernel.org
> Cc: kexec@...ts.infradead.org
> Cc: x86@...nel.org
> Cc: linux-arm-kernel@...ts.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 <bhe@...hat.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
>