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** Tags added: verification-needed-bionic

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https://bugs.launchpad.net/bugs/1797200

Title:
  [Bionic] ACPI / PPTT: use ACPI ID whenever
  ACPI_PPTT_ACPI_PROCESSOR_ID_VALID is set

Status in linux package in Ubuntu:
  Invalid
Status in linux source package in Bionic:
  Fix Committed

Bug description:
  [Impact]
  Currently, we use the ACPI processor ID only for the leaf/processor nodes as 
the specification states it must match the value of the ACPI processor ID field 
in the processor’s entry in the MADT.

  However, if a PPTT structure represents a processors group, it matches
  a processor container UID in the namespace and the
  ACPI_PPTT_ACPI_PROCESSOR_ID_VALID flag indicates whether the ACPI
  processor ID is valid.

  Let's use UID whenever ACPI_PPTT_ACPI_PROCESSOR_ID_VALID is set to be
  consistent instead of using table offset as it's currently done for
  non-leaf nodes.

  Fixes: 2bd00bcd73e5 (ACPI/PPTT: Add Processor Properties Topology
  Table parsing)

  [Fix]
  This patch in is 4.18:
  30998033f62a ACPI / PPTT: use ACPI ID whenever 
ACPI_PPTT_ACPI_PROCESSOR_ID_VALID is set

  [Test]
  -- testcase --

  #!/bin/bash

  stress-ng -q --vm 100 --vm-bytes 1G --cpu 210 --timeout 2400s --metrics-brief 
&
  pid=$!

  for i in {1..210}; do
        num=$((RANDOM%10+$i))
        echo "Offline CPU $num"
        echo 0 > /sys/devices/system/cpu/cpu$num/online || exit 1
        sleep 3s
        echo "Online CPU $num"
        echo 1 > /sys/devices/system/cpu/cpu$num/online || exit 1
  done

  kill -9 $pid
  ----------------
  Executed the test case with stock Bionic kernel and with Bionic kernel with 
patches applied. No system hang or crash was observed. On Cavium CN99XX Thunder 
X2 system. 

  [Regression Potential]
  Regression tested on Cavium Thunder X2 CN99XX system, and none were found. 
Regression risk is low.

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