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

[Bhupesh Sharma]

Changes since v1:
----------------
- v1 was sent out as a single patch which can be seen here:
  http://lists.infradead.org/pipermail/kexec/2019-February/022411.html

- 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@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Boris Petkov <bp@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Anderson <anderson@xxxxxxxxxx>
Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: kexec@xxxxxxxxxxxxxxxxxxx

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(+)

-- 
2.7.4