[PATCH v2 0/2] Append new variables to vmcoreinfo (PTRS_PER_PGD for arm64 and MAX_PHYSMEM_BITS for all archs)

Bhupesh Sharma bhsharma at redhat.com
Sun Mar 10 21:04:00 AEDT 2019

Changes since v1:
- v1 was sent out as a single patch which can be seen here:

- v2 breaks the single patch into two independent patches:
  [PATCH 1/2] appends 'PTRS_PER_PGD' to vmcoreinfo for arm64 arch, whereas
  [PATCH 2/2] appends 'MAX_PHYSMEM_BITS' to vmcoreinfo in core kernel code (all archs)

This patchset primarily fixes the regression reported in user-space
utilities like 'makedumpfile' and 'crash-utility' on arm64 architecture
with the availability of 52-bit address space feature in underlying
kernel. These regressions have been reported both on CPUs which don't
support ARMv8.2 extensions (i.e. LVA, LPA) and are running newer kernels
and also on prototype platforms (like ARMv8 FVP simulator model) which
support ARMv8.2 extensions and are running newer kernels.

The reason for these regressions is that right now user-space tools
have no direct access to these values (since these are not exported
from the kernel) and hence need to rely on a best-guess method of
determining value of 'PTRS_PER_PGD' and 'MAX_PHYSMEM_BITS' supported
by underlying kernel.

Exporting these values via vmcoreinfo will help user-land in such cases.
In addition, as per suggestion from makedumpfile maintainer (Kazu)
during v1 review, it makes more sense to append 'MAX_PHYSMEM_BITS' to
vmcoreinfo in the core code itself rather than in arm64 arch-specific
code, so that the user-space code for other archs can also benefit from
this addition to the vmcoreinfo and use it as a standard way of
determining 'SECTIONS_SHIFT' value in user-land.

Cc: Mark Rutland <mark.rutland at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Boris Petkov <bp at alien8.de>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Paul Mackerras <paulus at samba.org>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Dave Anderson <anderson at redhat.com>
Cc: Kazuhito Hagio <k-hagio at ab.jp.nec.com>
Cc: x86 at kernel.org
Cc: linuxppc-dev at lists.ozlabs.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Cc: kexec at lists.infradead.org

Bhupesh Sharma (2):
  arm64, vmcoreinfo : Append 'PTRS_PER_PGD' to vmcoreinfo
  crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo

 arch/arm64/kernel/crash_core.c | 1 +
 kernel/crash_core.c            | 1 +
 2 files changed, 2 insertions(+)


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