linux-kernel - Re: [PATCH v6 0/2] Append new variables to vmcoreinfo (TCR_EL1.T1SZ for arm64 and MAX_PHYSMEM

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Date:   Tue, 2 Jun 2020 10:54:46 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        x86@...nel.org
Cc:     Bhupesh SHARMA <bhupesh.linux@...il.com>,
        Boris Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        James Morse <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Steve Capper <steve.capper@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Dave Anderson <anderson@...hat.com>,
        Kazuhito Hagio <k-hagio@...jp.nec.com>,
        John Donnelly <john.p.donnelly@...cle.com>,
        scott.branden@...adcom.com, Amit Kachhap <amit.kachhap@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        kexec mailing list <kexec@...ts.infradead.org>
Subject: Re: [PATCH v6 0/2] Append new variables to vmcoreinfo (TCR_EL1.T1SZ
 for arm64 and MAX_PHYSMEM_BITS for all archs)

Hello,

On Thu, May 14, 2020 at 12:22 AM Bhupesh Sharma <bhsharma@...hat.com> wrote:
>
> Apologies for the delayed update. Its been quite some time since I
> posted the last version (v5), but I have been really caught up in some
> other critical issues.
>
> Changes since v5:
> ----------------
> - v5 can be viewed here:
>   http://lists.infradead.org/pipermail/kexec/2019-November/024055.html
> - Addressed review comments from James Morse and Boris.
> - Added Tested-by received from John on v5 patchset.
> - Rebased against arm64 (for-next/ptr-auth) branch which has Amit's
>   patchset for ARMv8.3-A Pointer Authentication feature vmcoreinfo
>   applied.
>
> Changes since v4:
> ----------------
> - v4 can be seen here:
>   http://lists.infradead.org/pipermail/kexec/2019-November/023961.html
> - Addressed comments from Dave and added patches for documenting
>   new variables appended to vmcoreinfo documentation.
> - Added testing report shared by Akashi for PATCH 2/5.
>
> Changes since v3:
> ----------------
> - v3 can be seen here:
>   http://lists.infradead.org/pipermail/kexec/2019-March/022590.html
> - Addressed comments from James and exported TCR_EL1.T1SZ in vmcoreinfo
>   instead of PTRS_PER_PGD.
> - Added a new patch (via [PATCH 3/3]), which fixes a simple typo in
>   'Documentation/arm64/memory.rst'
>
> Changes since v2:
> ----------------
> - v2 can be seen here:
>   http://lists.infradead.org/pipermail/kexec/2019-March/022531.html
> - Protected 'MAX_PHYSMEM_BITS' vmcoreinfo variable under CONFIG_SPARSEMEM
>   ifdef sections, as suggested by Kazu.
> - Updated vmcoreinfo documentation to add description about
>   'MAX_PHYSMEM_BITS' variable (via [PATCH 3/3]).
>
> 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 'vabits_actual' 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),
> 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: Boris Petkov <bp@...en8.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: James Morse <james.morse@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Steve Capper <steve.capper@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Dave Anderson <anderson@...hat.com>
> Cc: Kazuhito Hagio <k-hagio@...jp.nec.com>
> Cc: John Donnelly <john.p.donnelly@...cle.com>
> Cc: scott.branden@...adcom.com
> Cc: Amit Kachhap <amit.kachhap@....com>
> Cc: x86@...nel.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-doc@...r.kernel.org
> Cc: kexec@...ts.infradead.org
>
> Bhupesh Sharma (2):
>   crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo
>   arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo
>
>  Documentation/admin-guide/kdump/vmcoreinfo.rst | 16 ++++++++++++++++
>  arch/arm64/include/asm/pgtable-hwdef.h         |  1 +
>  arch/arm64/kernel/crash_core.c                 | 10 ++++++++++
>  kernel/crash_core.c                            |  1 +
>  4 files changed, 28 insertions(+)

Ping. @James Morse , Others

Please share if you have some comments regarding this patchset.

Thanks,
Bhupesh