Hi All,

On Wed, Jun 3, 2020 at 9:03 PM John Donnelly [off-list ref] wrote:

quoted

On Jun 3, 2020, at 8:20 AM, chenzhou [off-list ref] wrote:

Hi,


On 2020/6/3 19:47, Prabhakar Kushwaha wrote:

quoted

Hi Chen,

On Tue, Jun 2, 2020 at 8:12 PM John Donnelly [off-list ref] wrote:

quoted

quoted

On Jun 2, 2020, at 12:38 AM, Prabhakar Kushwaha [off-list ref] wrote:

On Tue, Jun 2, 2020 at 3:29 AM John Donnelly [off-list ref] wrote:

quoted

Hi .  See below !

quoted

On Jun 1, 2020, at 4:02 PM, Bhupesh Sharma [off-list ref] wrote:

Hi John,

On Tue, Jun 2, 2020 at 1:01 AM John Donnelly [off-list ref] wrote:

quoted

Hi,


On 6/1/20 7:02 AM, Prabhakar Kushwaha wrote:

quoted

Hi Chen,

On Thu, May 21, 2020 at 3:05 PM Chen Zhou [off-list ref] wrote:

quoted

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.

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 ,

quoted

quoted

quoted

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 “server class” Arm  equipment ?  Or auto-configured on boot ?  Consult an expert ;-)

quoted

quoted

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));

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

if you consider this as valid change,  can you please incorporate as
part of your patch-set.

After commit 1a8e1cef7 ("arm64: use both ZONE_DMA and ZONE_DMA32")，the 0-4G memory is splited
to DMA [mem 0x0000000000000000-0x000000003fffffff] and DMA32 [mem 0x0000000040000000-0x00000000ffffffff] on arm64.

From the above discussion, on your platform, the low crashkernel fall in DMA32 region, but your environment needs to access DMA
region, so there is the call trace.

I have a question, why do you choose 0xc0000000 here?

Besides, this is common code, we also need to consider about x86.

 + nsaenzjulienne@suse.de

  Exactly .  This is why it needs to be a CONFIG option for  Raspberry ..,  or device tree option.


  We could revert 1a8e1cef7 since it broke  Arm kdump too.

Well, unfortunately the patch for commit 1a8e1cef7603 ("arm64: use
both ZONE_DMA and ZONE_DMA32") was not Cc'ed to the kexec mailing
list, thus we couldn't get many eyes on it for a thorough review from
kexec/kdump p-o-v.

Also we historically never had distinction in common arch code on the
basis of the intended end use-case: embedded, server or automotive, so
I am not sure introducing a Raspberry specific CONFIG option would be
a good idea.

So, rather than reverting the patch, we can look at addressing the
same properly this time - especially from a kdump p-o-v.
This issue has been reported by some Red Hat arm64 partners with
upstream kernel also and as we have noticed in the past as well,
hardcoding the placement of the crashkernel base address (unless the
base address is specified by a crashkernel=X@Y like bootargs) is also
not a portable suggestion.

I am working on a possible fix and will have more updates on the same
in a day-or-two.

Thanks,
Bhupesh