From: Pingfan Liu kernelfans@gmail.com
commit 4f5aecdff25f59fb5ea456d5152a913906ecf287 upstream.
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 Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/crash_core.c | 1 + 1 file changed, 1 insertion(+)
--- a/kernel/crash_core.c +++ b/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);