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[Launchpad Bug Tracker <1857616@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package makedumpfile - 1:1.6.6-4ubuntu2

---------------
makedumpfile (1:1.6.6-4ubuntu2) focal; urgency=medium

  * x86_64: Fix an error due to makedumpfile being out-of-sync with recent
    kernels. To achieve that, add the following patch: "Increase
    SECTION_MAP_LAST_BIT to 4". (LP: #1857616)

 -- gpiccoli@xxxxxxxxxxxxx (Guilherme G. Piccoli)  Fri, 03 Jan 2020
16:57:00 -0300

** Changed in: makedumpfile (Ubuntu Focal)
       Status: Confirmed => Fix Released

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https://bugs.launchpad.net/bugs/1857616

Title:
  Cannot collect dump due to "Can't get a valid pmd_pte" error

Status in makedumpfile package in Ubuntu:
  Fix Released
Status in makedumpfile source package in Xenial:
  Opinion
Status in makedumpfile source package in Bionic:
  Confirmed
Status in makedumpfile source package in Disco:
  Invalid
Status in makedumpfile source package in Eoan:
  Confirmed
Status in makedumpfile source package in Focal:
  Fix Released

Bug description:
  [Impact]

  * Currently makedumpfile has 2 flaws due to: (a) out of
  synchronization with kernel code and, (b) kaslr handling. The first is
  related to a definition of a memory flag bit, whereas the second is
  about kaslr offset calculation - both cause similar failures when
  collecting the vmcore in kdump environment:

  Excluding unnecessary pages : [ 46.3 %] / __vtop4_x86_64[ 39.341233]: Can't get a valid pmd_pte.
  readmem: Can't convert a virtual address(ffffe05cb4000000) to physical address.
  readmem: type_addr: 0, addr:ffffe05cb4000000, size:32768
  __exclude_unnecessary_pages: Can't read the buffer of struct page.
  create_2nd_bitmap: Can't exclude unnecessary pages.

  * The report is mainly related to the first issue, which started to
  happen after the merge of kernel commit 326e1b8f83a4 ("mm/sparsemem:
  introduce a SECTION_IS_EARLY flag"), introduced in kernel 5.3. After
  this commit, a memory flag was changed and induced the error in dump
  collection. The fix is available in makedumpfile, as commit 7bdb468c2c
  ("Increase SECTION_MAP_LAST_BIT to 4"). This is hereby SRUed to Bionic
  (due to HWE kernel 5.3), Eoan and Focal.

  * The other issue is fixed in both Eoan and Focal, on makedumpfile
  1.6.6-based version. It is related with the kaslr offset: if the
  offset is small enough, we may return 0 wrongly in
  get_kaslr_offset_x86_64(), causing the vmcore collection to fail or
  even worse, to erase unintended data from the memory dump. This is
  fixed by makedumpfile commit 3222d4ad04 ("x86_64: fix
  get_kaslr_offset_x86_64() to return kaslr_offset correctly"), which
  isn't present in versions before 1.6.6. We hereby SRU this fix for
  Bionic.

  * Notice this modification is being worked concurrently with other
  kdump-tools' changes in LP #1828596.

  [Test Case]

  1) Deploy an Eoan VM e.g. with uvt-kvm;
  2) Set-up console output in the guest;
  3) Install the kdump-tools package;
  4) Configure and collect a dump (with sysrq to panic the system) - the error aforementioned is observed given Eoan kernel is 5.3-based.

  [Regression Potential]

  * The modifications hereby proposed are minimal and scope-constrained
  to makedumpfile in x86_64; both are merged in makedumpfile upstream,
  one of them being already released in E/F. An unlikely  regression
  would potentially fails vmcore collection in kdump environment.

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