+ crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch added to -mm tree

+ crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch added to -mm tree

[akpm]

The patch titled
     Subject: crash_core, vmcoreinfo: append 'SECTION_SIZE_BITS' to vmcoreinfo
has been added to the -mm tree.  Its filename is
     crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch

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------------------------------------------------------
From: Pingfan Liu <kernelfans@gmail.com>
Subject: crash_core, vmcoreinfo: append 'SECTION_SIZE_BITS' to vmcoreinfo

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.

Link: https://lkml.kernel.org/r/20210608103359.84907-1-kernelfans@gmail.com
Link: http://lists.infradead.org/pipermail/kexec/2021-June/022676.html
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Boris Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: James Morse <james.morse@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Dave Anderson <anderson@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/crash_core.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/crash_core.c~crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo
+++ a/kernel/crash_core.c
@@ -464,6 +464,7 @@ static int __init crash_save_vmcoreinfo_
 	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);
_

Patches currently in -mm which might be from kernelfans@gmail.com are

crash_core-vmcoreinfo-append-section_size_bits-to-vmcoreinfo.patch