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

[Bhupesh Sharma]

Hi Dave,

On 03/11/2019 02:35 PM, Dave Young wrote:
> Hi Bhupesh,
> On 03/10/19 at 03:34pm, Bhupesh Sharma wrote:
> > 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(+)
>
> Lianbo's document patch has been merged, would you mind to add vmcoreinfo doc
> patch as well in your series?

Thanks for the inputs. Will add it to the v3.
Let's wait for other comments/reviews, before I spin a version 3.

Regards,
Bhupesh