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From: Pingfan Liu <kernelfans@gmail.com>
Subject: [PATCH] crash_core,
 vmcoreinfo: Append 'SECTION_SIZE_BITS' to vmcoreinfo
Date: Tue,  8 Jun 2021 06:33:59 -0400
Message-Id: <20210608103359.84907-1-kernelfans@gmail.com>
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Cc: Pingfan Liu <kernelfans@gmail.com>, Bhupesh Sharma <bhupesh.sharma@linaro.org>, Kazuhito Hagio <k-hagio@ab.jp.nec.com>, Dave Young <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>, Boris Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>, James Morse <james.morse@arm.com>, Mark Rutland <mark.rutland@arm.com>, Will Deacon <will@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, Michael Ellerman <mpe@ellerman.id.au>, Paul Mackerras <paulus@samba.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Dave Anderson <anderson@redhat.com>, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org

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@gmail.com>
Cc: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Cc: Kazuhito Hagio <k-hagio@ab.jp.nec.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@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: linuxppc-dev@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org
Cc: kexec@lists.infradead.org
Cc: x86@kernel.org
Cc: linux-arm-kernel@lists.infradead.org
---
 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


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