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

[Prabhakar Kushwaha <prabhakar.pkin@gmail.com>]

On Tue, Jun 2, 2020 at 3:29 AM John Donnelly <john.p.donnelly@oracle.com> wrote:
>
> Hi .  See below !
>
> > On Jun 1, 2020, at 4:02 PM, Bhupesh Sharma <bhsharma@redhat.com> wrote:
> >
> > Hi John,
> >
> > On Tue, Jun 2, 2020 at 1:01 AM John Donnelly <John.P.donnelly@oracle.com> 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@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.
> >>>>
> >>>> 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 don’t 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

> I would like to see Chen’s 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));


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