linux-kernel - Re: [PATCH v2 0/2] Append new variables to vmcoreinfo (PTRS_PER_PGD for arm64 and MAX_PHYSMEM

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Message-ID: <20190311090553.GA12130@dhcp-128-65.nay.redhat.com>
Date:   Mon, 11 Mar 2019 17:05:53 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Bhupesh Sharma <bhsharma@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Kazuhito Hagio <k-hagio@...jp.nec.com>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org,
        Will Deacon <will.deacon@....com>,
        linuxppc-dev@...ts.ozlabs.org, kexec@...ts.infradead.org,
        James Morse <james.morse@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Boris Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>, bhupesh.linux@...il.com,
        Dave Anderson <anderson@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH v2 0/2] Append new variables to vmcoreinfo (PTRS_PER_PGD
 for arm64 and MAX_PHYSMEM_BITS for all archs)

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@....com>
> Cc: James Morse <james.morse@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Boris Petkov <bp@...en8.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> 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: kexec@...ts.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(+)
> 

Lianbo's document patch has been merged, would you mind to add vmcoreinfo doc
patch as well in your series?

Thanks
Dave