[makedumpfile PATCH v2] Always use bigger SECTION_MAP_MASK

[Masaki Tachibana]

Hi Petr,

Thank you for your V2 patch.
I will merge it into V1.6.4.

Thanks
Tachibana

> -----Original Message-----
> From: kexec [mailto:kexec-bounces at lists.infradead.org] On Behalf Of Petr Tesarik
> Sent: Tuesday, March 20, 2018 6:31 PM
> To: Tachibana Masaki() <mas-tachibana at vf.jp.nec.com>
> Cc: kexec mailing list <kexec at lists.infradead.org>
> Subject: [makedumpfile PATCH v2] Always use bigger SECTION_MAP_MASK
> 
> It is not necessary to distinguish between different kernel
> versions. Kernel commit 2d070eab2e82 merely reuses a previously
> unused bit (see clarification in kernel commit def9b71ee651a). The
> bit was always zero even before that commit, so it is safe to mask
> it off even for kernel versions before 4.13, removing some of the
> complexity.
> 
> More importantly, makedumpfile fails on kernels which backport the
> patch on top of an older version (for example SLES15).
> 
> Signed-off-by: Petr Tesarik <ptesarik at suse.com>
> ---
>  makedumpfile.c | 5 +----
>  makedumpfile.h | 9 ++++++++-
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/makedumpfile.c b/makedumpfile.c
> index ed138d3..b180eb3 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -3337,10 +3337,7 @@ section_mem_map_addr(unsigned long addr)
>  		return NOT_KV_ADDR;
>  	}
>  	map = ULONG(mem_section + OFFSET(mem_section.section_mem_map));
> -	if (info->kernel_version < KERNEL_VERSION(4, 13, 0))
> -		map &= SECTION_MAP_MASK_4_12;
> -	else
> -		map &= SECTION_MAP_MASK;
> +	map &= SECTION_MAP_MASK;
>  	free(mem_section);
> 
>  	return map;
> diff --git a/makedumpfile.h b/makedumpfile.h
> index 01eece2..8491025 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -185,8 +185,15 @@ isAnon(unsigned long mapping)
>  #define SECTION_ROOT_MASK()	(SECTIONS_PER_ROOT() - 1)
>  #define SECTION_NR_TO_ROOT(sec)	((sec) / SECTIONS_PER_ROOT())
>  #define SECTION_IS_ONLINE	(1UL<<2)
> +/*
> + * SECTION_MAP_LAST_BIT was 1UL<<2 before Linux 4.13.0.
> + * However, we always use the higher value, because:
> + *  1. at least one distributor backported commit 2d070eab2e82 to kernel
> + *     version 4.12,
> + *  2. it has been verified that (1UL<<2) was never set, so it is
> + *     safe to mask that bit off even in old kernels.
> + */
>  #define SECTION_MAP_LAST_BIT	(1UL<<3)
> -#define SECTION_MAP_MASK_4_12	(~(SECTION_IS_ONLINE-1))
>  #define SECTION_MAP_MASK	(~(SECTION_MAP_LAST_BIT-1))
>  #define NR_SECTION_ROOTS()	divideup(num_section, SECTIONS_PER_ROOT())
>  #define SECTION_NR_TO_PFN(sec)	((sec) << PFN_SECTION_SHIFT())
> --
> 2.13.6
> 
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