Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64 kdump

From: John Donnelly
Date: Tue Jun 02 2020 - 10:42:53 EST

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In reply to: Prabhakar Kushwaha: "Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64 kdump"
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> On Jun 2, 2020, at 12:38 AM, Prabhakar Kushwaha <prabhakar.pkin@xxxxxxxxx> wrote:
>
> On Tue, Jun 2, 2020 at 3:29 AM John Donnelly <john.p.donnelly@xxxxxxxxxx> wrote:
>>
>> Hi . See below !
>>
>>> On Jun 1, 2020, at 4:02 PM, Bhupesh Sharma <bhsharma@xxxxxxxxxx> wrote:
>>>
>>> Hi John,
>>>
>>> On Tue, Jun 2, 2020 at 1:01 AM John Donnelly <John.P.donnelly@xxxxxxxxxx> wrote:
>>>>
>>>> Hi,
>>>>
>>>>
>>>> On 6/1/20 7:02 AM, Prabhakar Kushwaha wrote:
>>>>> Hi Chen,
>>>>>
>>>>> On Thu, May 21, 2020 at 3:05 PM Chen Zhou <chenzhou10@xxxxxxxxxx> 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.
>>>>>>
>>>>>> 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, that is, 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 add DT property
>>>>>> "linux,low-memory-range" to crash dump kernel's dtb to pass the low region.
>>>>>>
>>>>>> Besides, we need to modify kexec-tools:
>>>>>> arm64: kdump: add another DT property to crash dump kernel's dtb(see [1])
>>>>>>
>>>>>> The previous changes and discussions can be retrieved from:
>>>>>>
>>>>>> 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]: https://urldefense.com/v3/__http://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbvpn1uM1$
>>>>>> [v1]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/2/1174__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbt0xN9PE$
>>>>>> [v2]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/9/86__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbub7yUQH$
>>>>>> [v3]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/9/306__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbnc4zPPV$
>>>>>> [v4]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/4/15/273__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbvsAsZLu$
>>>>>> [v5]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/5/6/1360__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbl24n-79$
>>>>>> [v6]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/8/30/142__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbs7r8G2a$
>>>>>> [v7]: https://urldefense.com/v3/__https://lkml.org/lkml/2019/12/23/411__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbiFUH90G$
>>>>>>
>>>>>> 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, low-memory-range
>>>>>> kdump: update Documentation about crashkernel on arm64
>>>>>> dt-bindings: chosen: Document linux,low-memory-range for arm64 kdump
>>>>>>
>>>>> We are getting "warn_alloc" [1] warning during boot of kdump kernel
>>>>> with bootargs as [2] of primary kernel.
>>>>> This error observed on ThunderX2 ARM64 platform.
>>>>>
>>>>> It is observed with latest upstream tag (v5.7-rc3) with this patch set
>>>>> and https://urldefense.com/v3/__https://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbiIAAlzu$
>>>>> Also **without** this patch-set
>>>>> "https://urldefense.com/v3/__https://www.spinics.net/lists/arm-kernel/msg806882.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbjC6ujMA$";
>>>>>
>>>>> This issue comes whenever crashkernel memory is reserved after 0xc000_0000.
>>>>> More details discussed earlier in
>>>>> https://urldefense.com/v3/__https://www.spinics.net/lists/arm-kernel/msg806882.html__;!!GqivPVa7Brio!LnTSARkCt0V0FozR0KmqooaH5ADtdXvs3mPdP3KRVqALmvSK2VmCkIPIhsaxbjC6ujMA$ without any
>>>>> solution
>>>>>
>>>>> This patch-set is expected to solve similar kind of issue.
>>>>> i.e. low memory is only targeted for DMA, swiotlb; So above mentioned
>>>>> observation should be considered/fixed. .
>>>>>
>>>>> --pk
>>>>>
>>>>> [1]
>>>>> [ 30.366695] DMI: Cavium Inc. Saber/Saber, BIOS
>>>>> TX2-FW-Release-3.1-build_01-2803-g74253a541a mm/dd/yyyy
>>>>> [ 30.367696] NET: Registered protocol family 16
>>>>> [ 30.369973] swapper/0: page allocation failure: order:6,
>>>>> mode:0x1(GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0
>>>>> [ 30.369980] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.7.0-rc3+ #121
>>>>> [ 30.369981] Hardware name: Cavium Inc. Saber/Saber, BIOS
>>>>> TX2-FW-Release-3.1-build_01-2803-g74253a541a mm/dd/yyyy
>>>>> [ 30.369984] Call trace:
>>>>> [ 30.369989] dump_backtrace+0x0/0x1f8
>>>>> [ 30.369991] show_stack+0x20/0x30
>>>>> [ 30.369997] dump_stack+0xc0/0x10c
>>>>> [ 30.370001] warn_alloc+0x10c/0x178
>>>>> [ 30.370004] __alloc_pages_slowpath.constprop.111+0xb10/0xb50
>>>>> [ 30.370006] __alloc_pages_nodemask+0x2b4/0x300
>>>>> [ 30.370008] alloc_page_interleave+0x24/0x98
>>>>> [ 30.370011] alloc_pages_current+0xe4/0x108
>>>>> [ 30.370017] dma_atomic_pool_init+0x44/0x1a4
>>>>> [ 30.370020] do_one_initcall+0x54/0x228
>>>>> [ 30.370027] kernel_init_freeable+0x228/0x2cc
>>>>> [ 30.370031] kernel_init+0x1c/0x110
>>>>> [ 30.370034] ret_from_fork+0x10/0x18
>>>>> [ 30.370036] Mem-Info:
>>>>> [ 30.370064] active_anon:0 inactive_anon:0 isolated_anon:0
>>>>> [ 30.370064] active_file:0 inactive_file:0 isolated_file:0
>>>>> [ 30.370064] unevictable:0 dirty:0 writeback:0 unstable:0
>>>>> [ 30.370064] slab_reclaimable:34 slab_unreclaimable:4438
>>>>> [ 30.370064] mapped:0 shmem:0 pagetables:14 bounce:0
>>>>> [ 30.370064] free:1537719 free_pcp:219 free_cma:0
>>>>> [ 30.370070] Node 0 active_anon:0kB inactive_anon:0kB
>>>>> active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB
>>>>> isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:0kB
>>>>> shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB
>>>>> unstable:0kB all_unreclaimable? no
>>>>> [ 30.370073] Node 1 active_anon:0kB inactive_anon:0kB
>>>>> active_file:0kB inactive_file:0kB unevictable:0kB isolated(anon):0kB
>>>>> isolated(file):0kB mapped:0kB dirty:0kB writeback:0kB shmem:0kB
>>>>> shmem_thp: 0kB shmem_pmdmapped: 0kB anon_thp: 0kB writeback_tmp:0kB
>>>>> unstable:0kB all_unreclaimable? no
>>>>> [ 30.370079] Node 0 DMA free:0kB min:0kB low:0kB high:0kB
>>>>> reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>>>> present:128kB managed:0kB mlocked:0kB kernel_stack:0kB pagetables:0kB
>>>>> bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
>>>>> [ 30.370084] lowmem_reserve[]: 0 250 6063 6063
>>>>> [ 30.370090] Node 0 DMA32 free:256000kB min:408kB low:664kB
>>>>> high:920kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>>>> present:269700kB managed:256000kB mlocked:0kB kernel_stack:0kB
>>>>> pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
>>>>> [ 30.370094] lowmem_reserve[]: 0 0 5813 5813
>>>>> [ 30.370100] Node 0 Normal free:5894876kB min:9552kB low:15504kB
>>>>> high:21456kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB
>>>>> active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB
>>>>> present:8388608kB managed:5953112kB mlocked:0kB kernel_stack:21672kB
>>>>> pagetables:56kB bounce:0kB free_pcp:876kB local_pcp:176kB free_cma:0kB
>>>>> [ 30.370104] lowmem_reserve[]: 0 0 0 0
>>>>> [ 30.370107] Node 0 DMA: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB
>>>>> 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
>>>>> [ 30.370113] Node 0 DMA32: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB
>>>>> 0*256kB 0*512kB 0*1024kB 1*2048kB (M) 62*4096kB (M) = 256000kB
>>>>> [ 30.370119] Node 0 Normal: 2*4kB (M) 3*8kB (ME) 2*16kB (UE) 3*32kB
>>>>> (UM) 1*64kB (U) 2*128kB (M) 2*256kB (ME) 3*512kB (ME) 3*1024kB (ME)
>>>>> 3*2048kB (UME) 1436*4096kB (M) = 5893600kB
>>>>> [ 30.370129] Node 0 hugepages_total=0 hugepages_free=0
>>>>> hugepages_surp=0 hugepages_size=1048576kB
>>>>> [ 30.370130] 0 total pagecache pages
>>>>> [ 30.370132] 0 pages in swap cache
>>>>> [ 30.370134] Swap cache stats: add 0, delete 0, find 0/0
>>>>> [ 30.370135] Free swap = 0kB
>>>>> [ 30.370136] Total swap = 0kB
>>>>> [ 30.370137] 2164609 pages RAM
>>>>> [ 30.370139] 0 pages HighMem/MovableOnly
>>>>> [ 30.370140] 612331 pages reserved
>>>>> [ 30.370141] 0 pages hwpoisoned
>>>>> [ 30.370143] DMA: failed to allocate 256 KiB pool for atomic
>>>>> coherent allocation
>>>>
>>>>
>>>> During my testing I saw the same error and Chen's solution corrected it .
>>>
>>> Which combination you are using on your side? I am using Prabhakar's
>>> suggested environment and can reproduce the issue
>>> with or without Chen's crashkernel support above 4G patchset.
>>>
>>> I am also using a ThunderX2 platform with latest makedumpfile code and
>>> kexec-tools (with the suggested patch
>>> <https://urldefense.com/v3/__https://lists.infradead.org/pipermail/kexec/2020-May/025128.html__;!!GqivPVa7Brio!J6lUig58-Gw6TKZnEEYzEeSU36T-1SqlB1kImU00xtX_lss5Tx-JbUmLE9TJC3foXBLg$ >).
>>>
>>> Thanks,
>>> Bhupesh
>>
>>
>> I did this activity 5 months ago and I have moved on to other activities. My DMA failures were related to PCI devices that could not be enumerated because low-DMA space was not available when crashkernel was moved above 4G; I donât recall the exact platform.
>>
>>
>>
>> For this failure ,
>>
>>>>> DMA: failed to allocate 256 KiB pool for atomic
>>>>> coherent allocation
>>
>>
>> Is due to :
>>
>>
>> 3618082c
>> ("arm64 use both ZONE_DMA and ZONE_DMA32")
>>
>> With the introduction of ZONE_DMA to support the Raspberry DMA
>> region below 1G, the crashkernel is placed in the upper 4G
>> ZONE_DMA_32 region. Since the crashkernel does not have access
>> to the ZONE_DMA region, it prints out call trace during bootup.
>>
>> It is due to having this CONFIG item ON :
>>
>>
>> CONFIG_ZONE_DMA=y
>>
>> Turning off ZONE_DMA fixes a issue and Raspberry PI 4 will
>> use the device tree to specify memory below 1G.
>>
>>
>
> Disabling ZONE_DMA is temporary solution. We may need proper solution

Perhaps the Raspberry platform configuration dependencies need separated from âserver classâ Arm equipment ? Or auto-configured on boot ? Consult an expert ;-)

>
>> I would like to see Chenâs feature added , perhaps as EXPERIMENTAL, so we can get some configuration testing done on it. It corrects having a DMA zone in low memory while crash-kernel is above 4GB. This has been going on for a year now.
>
> I will also like this patch to be added in Linux as early as possible.
>
> Issue mentioned by me happens with or without this patch.
>
> This patch-set can consider fixing because it uses low memory for DMA
> & swiotlb only.
> We can consider restricting crashkernel within the required range like below
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 7f9e5a6dc48c..bd67b90d35bd 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -354,7 +354,7 @@ int __init reserve_crashkernel_low(void)
> return 0;
> }
>
> - low_base = memblock_find_in_range(0, 1ULL << 32, low_size, CRASH_ALIGN);
> + low_base = memblock_find_in_range(0,0xc0000000, low_size, CRASH_ALIGN);
> if (!low_base) {
> pr_err("Cannot reserve %ldMB crashkernel low memory,
> please try smaller size.\n",
> (unsigned long)(low_size >> 20));
>
>

I suspect 0xc0000000 would need to be a CONFIG item and not hard-coded.

> Similar change can be considered for scenario "without" this patch.
> But it will decrease memory availability for crashkernel.
> Hence increase the failure probability of crashkernel reservation.
>
> --pk

Next message: James Bottomley: "Re: [PATCH v5 0/4] Introduce TEE based Trusted Keys support"
Previous message: Qian Cai: "Re: [PATCH 11/14] x86/entry: Clarify irq_{enter,exit}_rcu()"
In reply to: Prabhakar Kushwaha: "Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64 kdump"
Next in thread: Prabhakar Kushwaha: "Re: [PATCH v8 0/5] support reserving crashkernel above 4G on arm64 kdump"
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