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[Koichiro Den <2106564@xxxxxxxxxxxxxxxxxx>]

>From https://ubuntu.com/download/server/power (thanks @cypressyew for
pointing this!),

> Starting with Ubuntu 22.04 LTS, POWER9 and POWER10 processors are
supported.

so we can skip further investigation (unless the same issue will be
observed on Jammy or later, in which case the tags for this LP should be
updated.)

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https://bugs.launchpad.net/bugs/2106564

Title:
  powerpc/ptrace:{ptrace-tm-tar, ptrace-tm-spd-tar} fail with PPR
  discrepancy on certain instance types with B:hwe-5.4

Status in ubuntu-kernel-tests:
  New

Bug description:
  Failure observed on bionic linux-hwe-5.4 5.4.0-214.234~18.04.1
  (2025.03.17) on metal P9g-LPAR01kernel.

  The failure was consistently observed across three runs (3/3. 100%) on
  this machine.

  Log output:

      [powerpc/ptrace:ptrace-tm-tar]

        # selftests: powerpc/ptrace: ptrace-tm-tar
        # test: ptrace_tm_tar
        # tags: git_version:unknown
   (X1) # [User Read (Running)]          TAR: 40 PPR: 4000000000000 DSCR: 400
        # [Ptrace Read (Running)]        TAR: 20 PPR: 8000000000000 DSCR: 200
        # [Ptrace Read (Checkpointed)]   TAR: 10 PPR: 4000000000000 DSCR: 100
   (X2) # [Ptrace Write (Checkpointed)]  TAR: 40 PPR: 10000000000000 DSCR: 400
        # failure: ptrace_tm_tar
        not ok 1 selftests: powerpc/ptrace: ptrace-tm-tar # exit=1

      [powerpc/ptrace:ptrace-tm-spd-tar]

        # selftests: powerpc/ptrace: ptrace-tm-spd-tar
        # test: ptrace_tm_spd_tar
        # tags: git_version:unknown
   (X3) # [User Read (Running)]          TAR: 40 PPR: 18000000000000 DSCR: 400
        # [Ptrace Read (Running)]        TAR: 30 PPR: c000000000000 DSCR: 300
        # [Ptrace Read (Checkpointed)]   TAR: 10 PPR: 4000000000000 DSCR: 100
   (X4) # [Ptrace Write (Checkpointed)]  TAR: 40 PPR: 10000000000000 DSCR: 400
        # failure: ptrace_tm_spd_tar
        not ok 1 selftests: powerpc/ptrace: ptrace-tm-spd-tar # exit=1

  * At (X3) above, PPR shoud've been 10000000000000 (Normal) as set at (X4)
    as the transaction is aborted, but it was read as 18000000000000 (High).

    Neither tm_spd_tar() nor trace_tm_spd_tar() (via ptrace) set this value
    (i.e. or 3,3,3) inside or outside the transaction. Given this should be
    an LPAR guest from its naming, its hypervisor side might have done
    something unexpected.

  * At (X1) above, PPR should've been 10000000000000 (Normal) as set at (X2),
    but it was read as 4000000000000 (Very low).

    Even though (X1) indicates the possibility that only updated CPPR failed to
    be read by tm_tar()'s mfspr(SPRN_PPR) for some reason (*notice that TAR and
    DSCR values are correctly read by mfspr as shown in the log), it's likely
    that this is just a symptom caused by unexpected behavior from the
    hypervisor, as observed at (X3).

  Ref. kernel doc on POWER9 TM issues:
  https://www.kernel.org/doc/html/latest/arch/powerpc/transactional_memory.html#power9

  P9g-LPAR01kernel is a new test instance type, so this is likely not a regression introduced in this SRU cycle.
  This test passed on other environments over many SRU cycles.

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