[Crash-utility] [PATCH] arm64: handle 1GB block

[Johan.Erlandsson at sony.com]

Hi Lianbo

>>
>> With enough continuous physical memory we can have 1GB block. This have
>> been seen only in linear mapping region in kernel space. I have only
>> verified this for VM_L3_4K.
>>
>> reference: alloc_init_pud(), use_1G_block() [arch/arm64/mm/mmu.c]
>>
>For this situation, do you know how to reproduce it easily? Can you share
>your steps in detail?

I can try, one requirement is that you have memory aligned at 1 GB and 
size is at least 1 GB. Lets assume we have vmcore with physical memory
at 0x100000000 (1 GB aligned) with size at least 1 GB. Then from crash we
could do:

crash> ptov 100000000
VIRTUAL           PHYSICAL        
ffffffe900000000  100000000       

crash> vtop ffffffe900000000
VIRTUAL           PHYSICAL        
ffffffe900000000  100000000       

PAGE DIRECTORY: ffffff990f66c000
   PGD: ffffff990f66cd20 => 68000100000711
  PAGE: 100000000  (1GB)

     PTE        PHYSICAL   FLAGS
68000100000711  100000000  (VALID|SHARED|AF|PXN|UXN)

      PAGE               PHYSICAL      MAPPING       INDEX CNT FLAGS
ffffffbfa4000000        100000000 ffffffe97de59090       fe  2 20054 uptodate,lru,workingset,mappedtodisk

I hope that helps.

Regards
Johan

>BTW: I did the test, but I didn't enter into the kernel code path because
>that condition was not met.
>
># dmesg|grep -i huge
>[    0.000000] Kernel command line: BOOT_IMAGE=(hd0,gpt2)/vmlinuz-5.12.0-rc7+ root=/dev/mapper/rhel_gigabyte--r120--20-root ro arm->smmu.disable_bypass=n initcall_blacklist=gtdt_sbsa_gwdt_init iommu.passthrough=1 crashkernel=512M hugepagesz=1G hugepages=6 >debug_pagealloc=on rd.lvm.lv=rhel_gigabyte-r120-20/root rd.lvm.lv=rhel_gigabyte-r120-20/swap
>[    2.620634] HugeTLB registered 1.00 GiB page size, pre-allocated 6 pages
>
>Thanks.
>Lianbo