linux-kernel - Re: [PATCH v4 0/3] Append new variables to vmcoreinfo (TCR_EL1.T1SZ for arm64 and MAX_PHYSMEM

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Date:   Thu, 21 Nov 2019 11:20:47 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Bhupesh Sharma <bhsharma@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        linux-doc@...r.kernel.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Boris Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>, bhupesh.linux@...il.com,
        linux-arm-kernel@...ts.infradead.org,
        Kazuhito Hagio <k-hagio@...jp.nec.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Steve Capper <steve.capper@....com>, kexec@...ts.infradead.org,
        James Morse <james.morse@....com>,
        Dave Anderson <anderson@...hat.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v4 0/3] Append new variables to vmcoreinfo (TCR_EL1.T1SZ
 for arm64 and MAX_PHYSMEM_BITS for all archs)

On 11/11/19 at 01:31pm, Bhupesh Sharma wrote:
> 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: 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 (3):
>   crash_core, vmcoreinfo: Append 'MAX_PHYSMEM_BITS' to vmcoreinfo
>   arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo

Soft reminder:  the new introduced vmcoreinfo needs documentation

Please check Documentation/admin-guide/kdump/vmcoreinfo.rst

Thanks
Dave