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You have been subscribed to a public bug by Ioanna Alifieraki (joalif):

[Impact]

On some arm systems makedumpfile fails to translate virtual to physical addresses properly.
This may result in makedumpfile looping forever exhausting
all memory, or  translating a virtual address to an invalid physical address 
and then failing and falling back to cp.
The reason it cannot resolve some addresses is because the PMD mask is wrong. 
When physical address mask allows up to 48bits pmd mask should allow the
same, currently pmd mask is set to 40bits (see commit [1]).

Commit [1] fixes this bug.

[Test Case]

To hit this bug you need a system that needs physical addresses over 1TB.
This may be either because you have a lot
of memory or because the firmware mapped some memory above 1TB for some
reason [1].

A user hit this bug because firmware mapped memory above 1TB and provided a 
dump so I could reproduce the bug when running makedumpfile on the dump.

[Regression Potential]

This commit changes the PMD_SECTION_MASK for arm64. So any regression potential
would only affect arm64 systems. In addition PMD_SECTION_MASK is used in translation
from virtual to physical addresses and therefore any regression would happen during
this process.

[Other]

[1]
https://github.com/makedumpfile/makedumpfile/commit/7242ae4cb5288df626f464ced0a8b60fd669100b


When testing kdump on Ubuntu 18.04.4 (arm64) GA kernel, makedumpfile fails. The test steps are as follows:
# echo 1> / proc / sys / kernel / sysrq
# echo c> / proc / sysrq-trigger
The logs are as follows:

kdump-tools[646]: starting kdump-tools: * running makedumpfile -c -d 31 /proc/vmcore /var/crash/202003251128/dump-incomplete
kdump-tools[646]: readpage_elf: Attempt to read non-existent page at 0x0
kdump-tools[646]: readmem: type_addr: 1, addr:ff0, size:8
kdump-tools[646]: vaddr_to_paddr_arm64: Can't read pud
kdump-tools[646]: readmem: Can't convert a virtual address(ffff9e653690) to physical address.
kdump-tools[646]: readmem: type_addr: 0, addr:ffff9e653690, size:1032
kdump-tools[646]: validate_mem_section: Can't read mem_section array.
kdump-tools[646]: get_mem_section: Could not validate mem_section.
kdump-tools[646]: get_mm_sparsemem: Can't get the address of mem_section.
kdump-tools[646]: makedumpfile Failed.
kdump-tools[646]: * kdump-tools: makedumpfile failed, falling back to 'cp'

But when I use the HWE kernel, I find that there is no such problem.
The HEW kernel version: 5.3.0-42-generic

** Affects: linux (Ubuntu)
     Importance: Medium
     Assignee: Ioanna Alifieraki (joalif)
         Status: Confirmed

** Affects: linux (Ubuntu Xenial)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu Bionic)
     Importance: Medium
     Assignee: Ioanna Alifieraki (joalif)
         Status: Confirmed

** Affects: linux (Ubuntu Eoan)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu Focal)
     Importance: Undecided
         Status: New

** Affects: linux (Ubuntu Groovy)
     Importance: Medium
     Assignee: Ioanna Alifieraki (joalif)
         Status: Confirmed

** Affects: linux (Debian)
     Importance: Unknown
         Status: Unknown


** Tags: sts
-- 
Kdump-Tools: Makedumpfile Failed, Falling Back To 'Cp'
https://bugs.launchpad.net/bugs/1869465
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