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Subject: Re: [PATCH v10 0/5] support reserving crashkernel above 4G on arm64
 kdump
To:     Bhupesh Sharma <bhsharma@redhat.com>
References: <20200703035816.31289-1-chenzhou10@huawei.com>
 <CACi5LpP+kFLv97guJ126xKk4_mfy2nFMp36KnDiXxPZ1ya2jPg@mail.gmail.com>
CC:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        RuiRui Yang <dyoung@redhat.com>, Baoquan He <bhe@redhat.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        James Morse <james.morse@arm.com>,
        Rob Herring <robh+dt@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        John Donnelly <John.P.donnelly@oracle.com>,
        "Prabhakar Kushwaha" <prabhakar.pkin@gmail.com>,
        <nsaenzjulienne@suse.de>, "Jonathan Corbet" <corbet@lwn.net>,
        Simon Horman <horms@verge.net.au>, <guohanjun@huawei.com>,
        <xiexiuqi@huawei.com>, <huawei.libin@huawei.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
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From:   chenzhou <chenzhou10@huawei.com>
Message-ID: <989e3b4f-4827-bb0f-5c3d-d9669c081c88@huawei.com>
Date:   Fri, 3 Jul 2020 16:38:15 +0800
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Hi Bhupesh,


On 2020/7/3 15:26, Bhupesh Sharma wrote:
> Hi Chen,
>
> On Fri, Jul 3, 2020 at 9:24 AM Chen Zhou <chenzhou10@huawei.com> wrote:
>> This patch series enable reserving crashkernel above 4G in arm64.
>>
>> There are following issues in arm64 kdump:
>> 1. We use crashkernel=X to reserve crashkernel below 4G, which will fail
>> when there is no enough low memory.
>> 2. Currently, crashkernel=Y@X can be used to reserve crashkernel above 4G,
>> in this case, if swiotlb or DMA buffers are required, crash dump kernel
>> will boot failure because there is no low memory available for allocation.
>> 3. commit 1a8e1cef7603 ("arm64: use both ZONE_DMA and ZONE_DMA32") broken
>> the arm64 kdump. If the memory reserved for crash dump kernel falled in
>> ZONE_DMA32, the devices in crash dump kernel need to use ZONE_DMA will alloc
>> fail.
>>
>> To solve these issues, introduce crashkernel=X,low to reserve specified
>> size low memory.
>> Crashkernel=X tries to reserve memory for the crash dump kernel under
>> 4G. If crashkernel=Y,low is specified simultaneously, reserve spcified
>> size low memory for crash kdump kernel devices firstly and then reserve
>> memory above 4G.
>>
>> When crashkernel is reserved above 4G in memory and crashkernel=X,low
>> is specified simultaneously, kernel should reserve specified size low memory
>> for crash dump kernel devices. So there may be two crash kernel regions, one
>> is below 4G, the other is above 4G.
>> In order to distinct from the high region and make no effect to the use of
>> kexec-tools, rename the low region as "Crash kernel (low)", and pass the
>> low region by reusing DT property "linux,usable-memory-range". We made the low
>> memory region as the last range of "linux,usable-memory-range" to keep
>> compatibility with existing user-space and older kdump kernels.
>>
>> Besides, we need to modify kexec-tools:
>> arm64: support more than one crash kernel regions(see [1])
>>
>> Another update is document about DT property 'linux,usable-memory-range':
>> schemas: update 'linux,usable-memory-range' node schema(see [2])
>>
>> The previous changes and discussions can be retrieved from:
>>
>> Changes since [v9]
>> - Patch 1 add Acked-by from Dave.
>> - Update patch 5 according to Dave's comments.
>> - Update chosen schema.
>>
>> Changes since [v8]
>> - Reuse DT property "linux,usable-memory-range".
>> Suggested by Rob, reuse DT property "linux,usable-memory-range" to pass the low
>> memory region.
>> - Fix kdump broken with ZONE_DMA reintroduced.
>> - Update chosen schema.
>>
>> Changes since [v7]
>> - Move x86 CRASH_ALIGN to 2M
>> Suggested by Dave and do some test, move x86 CRASH_ALIGN to 2M.
>> - Update Documentation/devicetree/bindings/chosen.txt.
>> Add corresponding documentation to Documentation/devicetree/bindings/chosen.txt
>> suggested by Arnd.
>> - Add Tested-by from Jhon and pk.
>>
>> Changes since [v6]
>> - Fix build errors reported by kbuild test robot.
>>
>> Changes since [v5]
>> - Move reserve_crashkernel_low() into kernel/crash_core.c.
>> - Delete crashkernel=X,high.
>> - Modify crashkernel=X,low.
>> If crashkernel=X,low is specified simultaneously, reserve spcified size low
>> memory for crash kdump kernel devices firstly and then reserve memory above 4G.
>> In addition, rename crashk_low_res as "Crash kernel (low)" for arm64, and then
>> pass to crash dump kernel by DT property "linux,low-memory-range".
>> - Update Documentation/admin-guide/kdump/kdump.rst.
>>
>> 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/2020-June/020737.html
>> [2]: https://github.com/robherring/dt-schema/pull/19
>> [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
>> [v5]: https://lkml.org/lkml/2019/5/6/1360
>> [v6]: https://lkml.org/lkml/2019/8/30/142
>> [v7]: https://lkml.org/lkml/2019/12/23/411
>> [v8]: https://lkml.org/lkml/2020/5/21/213
>> [v9]: https://lkml.org/lkml/2020/6/28/73
>>
>> Chen Zhou (5):
>>   x86: kdump: move reserve_crashkernel_low() into crash_core.c
>>   arm64: kdump: reserve crashkenel above 4G for crash dump kernel
>>   arm64: kdump: add memory for devices by DT property
>>     linux,usable-memory-range
>>   arm64: kdump: fix kdump broken with ZONE_DMA reintroduced
>>   kdump: update Documentation about crashkernel on arm64
>>
>>  Documentation/admin-guide/kdump/kdump.rst     | 14 ++-
>>  .../admin-guide/kernel-parameters.txt         | 17 +++-
>>  arch/arm64/kernel/setup.c                     |  8 +-
>>  arch/arm64/mm/init.c                          | 74 ++++++++++++---
>>  arch/x86/kernel/setup.c                       | 66 ++------------
>>  include/linux/crash_core.h                    |  3 +
>>  include/linux/kexec.h                         |  2 -
>>  kernel/crash_core.c                           | 90 +++++++++++++++++++
>>  kernel/kexec_core.c                           | 17 ----
>>  9 files changed, 197 insertions(+), 94 deletions(-)
>>
>> --
>> 2.20.1
> Thanks for the v10.
>
> 1. Seems this series is still broken on arm64 boards like ampere and
> ThunderX2 (marvell) because of the ZONE_DMA32 related OOM seen while
> booting kdump kernel.
> Here are details about my environment:
>
> - Latest upstream Linus master branch (5.8.0-rc3) + your v10 patches.
> - Latest upstream kexec-tools + your v4 patch.
>
> # dmesg | grep -i crash
> [    0.000000] crashkernel reserved: 0x00000000ca000000 -
> 0x00000000ea000000 (512 MB)
> [    0.000000] Kernel command line:
> BOOT_IMAGE=(hd13,gpt2)/vmlinuz-5.8.0-rc3+
> root=/dev/mapper/rhel_hpe--apache--cn99xx--09-root ro
> rd.lvm.lv=rhel_hpe-apache-cn99xx-09/root
> rd.lvm.lv=rhel_hpe-apache-cn99xx-09/swap crashkernel=512M
> [   58.917523]     crashkernel=512M
>
> 2. Here is the OOM crash seen while booting the kdump kernel:
>
> [    0.244724] DMA: preallocated 128 KiB GFP_KERNEL pool for atomic allocations
> [    0.251859] Unable to handle kernel NULL pointer dereference at
> virtual address 0000000000000188
> [    0.260737] Mem abort info:
> [    0.263553]   ESR = 0x96000006
> [    0.266632]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    0.271994]   SET = 0, FnV = 0
> [    0.275074]   EA = 0, S1PTW = 0
> [    0.278239] Data abort info:
> [    0.281141]   ISV = 0, ISS = 0x00000006
> [    0.285010]   CM = 0, WnR = 0
> [    0.288001] [0000000000000188] user address but active_mm is swapper
> [    0.294420] Internal error: Oops: 96000006 [#1] SMP
> [    0.299344] Modules linked in:
> [    0.302424] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.8.0-rc3+ #8
> [    0.308753] Hardware name: HPE Apollo 70             /C01_APACHE_MB
>         , BIOS L50_5.13_1.11 06/18/2019
> [    0.318599] pstate: 00400009 (nzcv daif +PAN -UAO BTYPE=--)
> [    0.324228] pc : mem_cgroup_get_nr_swap_pages+0x2c/0x60
> [    0.329506] lr : shrink_lruvec+0x404/0x4f8
> [    0.333638] sp : fffffe0012b8f840
> [    0.336979] x29: fffffe0012b8f840 x28: fffffe00116b3000
> [    0.342343] x27: fffffe0012b8fb00 x26: 0000000000000020
> [    0.347707] x25: 0000000000000000 x24: fffffc0069fffe28
> [    0.353070] x23: 0000000000000000 x22: 0000000000000000
> [    0.358433] x21: 000000000000003c x20: fffffe0012b8fa98
> [    0.363796] x19: 0000000000000000 x18: 0000000000000010
> [    0.369159] x17: 00000000bd8afee8 x16: 000000001260aa76
> [    0.374523] x15: ffffffffffffffff x14: fffffe00116b3988
> [    0.379886] x13: fffffe0092b8faa7 x12: fffffe0012b8faaf
> [    0.385248] x11: fffffe00116f1000 x10: fffffe0012b8fa30
> [    0.390612] x9 : fffffe0010244ebc x8 : 0000000000000000
> [    0.395975] x7 : 0000000000000020 x6 : 00000000ffff8ae3
> [    0.401338] x5 : 0000000000000000 x4 : fffffc004da89000
> [    0.406701] x3 : 0000000000000000 x2 : 0000000000000000
> [    0.412064] x1 : fffffe00116bf000 x0 : 0000000000000000
> [    0.417427] Call trace:
> [    0.419891]  mem_cgroup_get_nr_swap_pages+0x2c/0x60
> [    0.424815]  shrink_node+0x1a8/0x688
> [    0.428420]  do_try_to_free_pages+0xe8/0x448
> [    0.432729]  try_to_free_pages+0x110/0x230
> [    0.436863]  __alloc_pages_slowpath.constprop.106+0x2b8/0xb48
> [    0.442666]  __alloc_pages_nodemask+0x2ac/0x2f8
> [    0.447239]  alloc_page_interleave+0x20/0x90
> [    0.451548]  alloc_pages_current+0xdc/0xf8
> [    0.455681]  atomic_pool_expand+0x60/0x210
> [    0.459817]  __dma_atomic_pool_init+0x50/0xa4
> [    0.464214]  dma_atomic_pool_init+0xac/0x158
> [    0.468522]  do_one_initcall+0x50/0x218
> [    0.472393]  kernel_init_freeable+0x22c/0x2d0
> [    0.476792]  kernel_init+0x18/0x110
> [    0.480310]  ret_from_fork+0x10/0x18
> [    0.483918] Code: 350001e3 d503201f f9450024 1400000a (f940c401)
> [    0.490074] ---[ end trace e5a9147af159e580 ]---
> [    0.494734] Kernel panic - not syncing: Fatal exception
> [    0.500010] Rebooting in 10 seconds..
>
> 3. Did you test your patch with a simple crashkernel=512M command line
> (without using the crashkernel hi/lo or crashkernel=X@Y format)?
>
> Anyway, since this implementation still needs rework, we can go ahead
> with the arrangement of limiting the crashkernel allocation in
> ZONE_DMA range (as I suggested in another patch series
> <http://lists.infradead.org/pipermail/kexec/2020-July/020777.html>) in
> the meanwhile. to ensure the upstream kernel can still support kdump
> on arm64 boards where it was working before the ZONE_DMA32 changes
> were introduced for arm64.
>
> Please let me know your views,
Thanks for your test and sharing your views. I have no questions about the 1 and 2 you mentioned.

I charity the issue in my patch 4 and suggest to use the parameter like
"crashkernel=X crashkernel=Y,low" if CONFIG_ZONE_DMA is enabled.
I also document this in doc in patch 5.

I choose to address the issue based on the  "reserving crashkernel above 4G",
because we just need to adjust the low memory limit instead of limiting the
whole crahshkernel to ZONE_DMA.
details: https://lkml.org/lkml/2020/7/3/64

But you are right, arm64 kdump is broken for long time, including the issue you addressed
"Append new variables to vmcoreinfo (TCR_EL1.T1SZ for arm64 and MAX_PHYSMEM_BITS for all archs)".

I agree with you to make it work as soon as possible.

Ping James, Will,
any other comments about this patch series?

Thanks,
Chen Zhou
>
> Thanks,
> Bhupesh
>
>
> .
>