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

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Date:   Tue, 12 Mar 2019 19:54:49 +0530
From:   Bhupesh Sharma <bhsharma@...hat.com>
To:     Dave Young <dyoung@...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 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@....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 for the inputs. Will add it to the v3.
Let's wait for other comments/reviews, before I spin a version 3.

Regards,
Bhupesh