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Subject: Re: [PATCH 0/4] support reserving crashkernel above 4G on arm64 kdump
To:     Chen Zhou <chenzhou10@huawei.com>, catalin.marinas@arm.com,
        will.deacon@arm.com, akpm@linux-foundation.org,
        ard.biesheuvel@linaro.org, rppt@linux.ibm.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, ebiederm@xmission.com
Cc:     wangkefeng.wang@huawei.com, linux-mm@kvack.org,
        kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
        takahiro.akashi@linaro.org, horms@verge.net.au,
        linux-arm-kernel@lists.infradead.org,
        "kexec@lists.infradead.org" <kexec@lists.infradead.org>,
        Bhupesh SHARMA <bhupesh.linux@gmail.com>
References: <20190507035058.63992-1-chenzhou10@huawei.com>
From:   Bhupesh Sharma <bhsharma@redhat.com>
Message-ID: <a9d017d0-82d3-3e5f-4af2-4c611393106d@redhat.com>
Date:   Wed, 15 May 2019 10:36:24 +0530
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+Cc kexec-list.

Hi Chen,

I think we are still in the quiet period of the merge cycle, but this is 
a change which will be useful for systems like HPE Apollo where we are 
looking at reserving crashkernel across a larger range.

Some comments inline and in respective patch threads..

On 05/07/2019 09:20 AM, Chen Zhou wrote:
> This patch series enable reserving crashkernel on high memory in arm64.

Please fix the patch subject, it should be v5.
Also please Cc the kexec-list (kexec@lists.infradead.org) for future 
versions to allow wider review of the patchset.

> We use crashkernel=X to reserve crashkernel below 4G, which will fail
> when there is no enough memory. Currently, crashkernel=Y@X can be used
> to reserve crashkernel above 4G, in this case, if swiotlb or DMA buffers
> are requierd, capture kernel will boot failure because of no low memory.

... ^^ required

s/capture kernel will boot failure because of no low memory./capture 
kernel boot will fail because there is no low memory available for 
allocation.

> When crashkernel is reserved above 4G in memory, kernel should reserve
> some amount of low memory for swiotlb and some DMA buffers. So there may
> be two crash kernel regions, one is below 4G, the other is above 4G. Then
> Crash dump kernel reads more than one crash kernel regions via a dtb
> property under node /chosen,
> linux,usable-memory-range = <BASE1 SIZE1 [BASE2 SIZE2]>.

Please use consistent naming for the second kernel, better to use crash 
dump kernel.

I have tested this on my HPE Apollo machine and with 
crashkernel=886M,high syntax, I can get the board to reserve a larger 
memory range for the crashkernel (i.e. 886M):

# dmesg | grep -i crash
[    0.000000] kexec_core: Reserving 256MB of low memory at 3560MB for 
crashkernel (System low RAM: 2029MB)
[    0.000000] crashkernel reserved: 0x0000000bc5a00000 - 
0x0000000bfd000000 (886 MB)

kexec/kdump can also work also work fine on the board.

So, with the changes suggested in this cover letter and individual 
patches, please feel free to add:

Reviewed-and-Tested-by: Bhupesh Sharma <bhsharma@redhat.com>

Thanks,
Bhupesh

> Besides, we need to modify kexec-tools:
>    arm64: support more than one crash kernel regions(see [1])
> 
> I post this patch series about one month ago. The previous changes and
> discussions can be retrived from:
> 
> Changes since [v4]
> - reimplement memblock_cap_memory_ranges for multiple ranges by Mike.
> 
> Changes since [v3]
> - Add memblock_cap_memory_ranges back for multiple ranges.
> - Fix some compiling warnings.
> 
> Changes since [v2]
> - Split patch "arm64: kdump: support reserving crashkernel above 4G" as
>    two. Put "move reserve_crashkernel_low() into kexec_core.c" in a separate
>    patch.
> 
> Changes since [v1]:
> - Move common reserve_crashkernel_low() code into kernel/kexec_core.c.
> - Remove memblock_cap_memory_ranges() i added in v1 and implement that
>    in fdt_enforce_memory_region().
>    There are at most two crash kernel regions, for two crash kernel regions
>    case, we cap the memory range [min(regs[*].start), max(regs[*].end)]
>    and then remove the memory range in the middle.
> 
> [1]: http://lists.infradead.org/pipermail/kexec/2019-April/022792.html
> [v1]: https://lkml.org/lkml/2019/4/2/1174
> [v2]: https://lkml.org/lkml/2019/4/9/86
> [v3]: https://lkml.org/lkml/2019/4/9/306
> [v4]: https://lkml.org/lkml/2019/4/15/273
> 
> Chen Zhou (3):
>    x86: kdump: move reserve_crashkernel_low() into kexec_core.c
>    arm64: kdump: support reserving crashkernel above 4G
>    kdump: update Documentation about crashkernel on arm64
> 
> Mike Rapoport (1):
>    memblock: extend memblock_cap_memory_range to multiple ranges
> 
>   Documentation/admin-guide/kernel-parameters.txt |  6 +--
>   arch/arm64/include/asm/kexec.h                  |  3 ++
>   arch/arm64/kernel/setup.c                       |  3 ++
>   arch/arm64/mm/init.c                            | 72 +++++++++++++++++++------
>   arch/x86/include/asm/kexec.h                    |  3 ++
>   arch/x86/kernel/setup.c                         | 66 +++--------------------
>   include/linux/kexec.h                           |  5 ++
>   include/linux/memblock.h                        |  2 +-
>   kernel/kexec_core.c                             | 56 +++++++++++++++++++
>   mm/memblock.c                                   | 44 +++++++--------
>   10 files changed, 157 insertions(+), 103 deletions(-)
>